Allied Health SAC 2

Endocrine System

Homeostasis

• Homeostasis refers to the body’s ability to maintain stable internal conditions.

• It is essential for survival and normal functioning.

• The endocrine system works alongside the nervous system to maintain homeostasis.

Comparison of Nervous vs Endocrine Systems

Nervous System

• Fast‑acting control system.

• Uses electrical nerve impulses.

• Produces immediate responses.

• Controls muscles and glands rapidly.

Endocrine System

• Slow‑acting control system.

• Uses chemical messengers called hormones.

• Hormones travel through the bloodstream.

• Effects are slower but longer lasting.

Major Functions of the Endocrine System

• Growth and development.

• Defence against stress.

• Reproduction.

• Maintenance of electrolyte balance.

• Regulation of metabolism.

Hormones

• Hormones are chemical substances secreted by endocrine cells.

• They regulate metabolic activity of other cells.

Types of Hormones

Amino Acid–Based Hormones

• Protein‑based molecules.

Steroid Hormones

• Include sex hormones.

• Produced by ovaries and testes.

Mechanisms of Hormone Action

Transport and Specificity

• Hormones circulate throughout the entire bloodstream.

Only certain cells respond — these are target cells.

Receptor Sites

• Target cells have specific receptor sites for specific hormones.

• Lock‑and‑key mechanism:

  • Hormone = key

  • Receptor = lock

  • If the hormone fits, a reaction occurs.

  • If it does not fit, no reaction occurs.

Target Organs

• When target cells are grouped into one organ, it is called a target organ.

Hormone Regulation

Potency

• Hormones are extremely potent.

• Very small amounts can cause major physiological changes.

Negative Feedback Mechanisms

• Primary method of hormone regulation.

• A gland detects the concentration of the substance it controls.

• If levels move away from normal, the gland triggers a response to reverse the change.

• Example: If body temperature rises, mechanisms activate to lower it.

Hormonal Cascades

• Some glands release hormones in response to other hormones.

Major Endocrine Organs

• Pituitary gland

• Thyroid gland

• Adrenal glands

• Thymus

• Pineal gland

• Pancreas

• Gonads (ovaries and testes)

• Hypothalamus (nervous system structure with endocrine function)

Pituitary Gland

Structure

• Size of a pea.

• Located on the inferior surface of the brain.

• Hangs from the hypothalamus.

• Two lobes:

  • Anterior pituitary (adenohypophysis) — glandular tissue

  • Posterior pituitary (neurohypophysis) — nervous tissue

Control

• Hypothalamus controls pituitary hormone release via releasing and inhibiting hormones.

Anterior Pituitary Hormones

Posterior Pituitary Hormones

Oxytocin

• Released in large amounts during childbirth.

• Stimulates strong uterine contractions.

Antidiuretic Hormone (ADH)

• Causes kidneys to reabsorb water.

• Reduces urine formation.

Thyroid Gland

Location

• Base of the throat.

• Two lobes connected by the isthmus.

Hormones Produced

Thyroid Hormone

• Contains iodine.

• Controls rate of glucose use.

• Converts glucose to heat and chemical energy.

• Essential for tissue growth and development.

• Especially important for reproductive and nervous system development.

Calcitonin

• Decreases blood calcium levels.

• Opposes parathyroid hormone.

Parathyroid Glands

Parathyroid Hormone (PTH)

• Controls blood calcium levels.

• Calcium is essential for:

  • Nerve function

  • Muscle contraction

  • Bone strength

  • Heart function

  • Kidney function

• Excess PTH → calcium removed from bones → increased risk of osteoporosis.

Thymus Gland

Location

• Upper thorax, behind sternum.

Function

Larger in infants and children.

• Shrinks with age.

• Produces thymosin.

• Thymosin is essential for development of T‑cells.

• T‑cells are vital for immune function.

Pineal Gland

Structure

• Small, cone‑shaped gland.

• Hangs from the roof of the brain.

Hormone: Melatonin

• Secreted into cerebrospinal fluid.

• Regulates sleep–wake cycles.

• Highest at night → induces drowsiness.

• Lowest during the day.

Helps regulate mood.

Adrenal Glands

Structure

• Sit on top of kidneys.

• Two regions:

  • Adrenal cortex (outer)

  • Adrenal medulla (inner)

Regulation

• Cortex: controlled by negative feedback via hypothalamus.

• Medulla: controlled by nerve impulses from hypothalamus.

Adrenal Cortex Hormones (Corticosteroids)

1. Mineralocorticoids

• Main hormone: Aldosterone

• Regulates sodium and potassium levels in the blood.

2. Glucocorticoids

• Promote normal cell metabolism.

• Help body manage increased blood glucose levels.

3. Sex Hormones

• Oestrogen and androgens.

• Support reproductive system function.

Adrenal Medulla Hormones

Epinephrine (Adrenaline) & Norepinephrine (Noradrenaline)

• Released during stress.

• Produce the fight‑or‑flight response:

  • Increased heart rate

  • Increased blood pressure

  • Dilated lung capillaries

Pancreas

Location

• Lies along abdominal cavity, below liver.

Functions

Exocrine Function

• Produces digestive enzymes.

• Enzymes travel through ducts to the duodenum.

Endocrine Function

• Pancreatic islets produce hormones.

Hormones

Glucagon (alpha cells)

• Released when blood glucose is low.

Insulin (beta cells)

• Released when blood glucose is high.

 Ovaries

Location

• Pelvic cavity.

Hormones

Oestrogen

• Development of female reproductive organs.

• Female secondary sex characteristics:

  • Breast development

  • Fat distribution in hips and legs

Progesterone

• Builds uterine lining for pregnancy.

Testes

Location

• Scrotum, outside pelvic cavity.

Hormone:

Testosterone

• Growth of male reproductive organs.

• Male secondary sex characteristics:

  • Facial hair

  • Muscle growth

  • Deepening of voice

Calcium Reabsorption

Vitamin D and parathyroid hormone (PTH) help regulate how much calcium is absorbed and how much calcium the kidneys eliminate. Healthy kidneys turn vitamin D into an active hormone (calcitriol), which helps increase calcium absorption from the intestines into the blood.

Differences Between Glands

Differences Between Hormones

Disorders of the Endocrine System

Causes

1. Hormone imbalance (too much or too little).

2. Tumours or cancers affecting endocrine glands.

Diabetes

• High blood glucose.

• Type 1: pancreas cannot produce insulin.

• Type 2: cells don’t respond properly; inadequate insulin.

• Symptoms:

  • Excessive thirst

  • Mood swings

  • Frequent urination

  • Weight loss

  • Vomiting

Hypoglycaemia

• Low blood glucose.

• Usually occurs in people with diabetes.

• Symptoms:

  • Fatigue

  • Anxiety

  • Pale skin

  • Heart palpitations

  • Tingling around mouth

• Severe cases:

  • Seizures

  • Blurred vision

  • Unconsciousness

Hyperthyroidism

• Overactive thyroid → too much thyroid hormone.

• Symptoms:

  • Excessive weight loss

  • Increased heart rate

  • Sweating

  • Anxiety

  • Bulging eyes

  • Enlarged thyroid

Goitre

• Enlargement of thyroid gland.

• Causes:

  • Iodine deficiency

  • Thyroid cancer

  • Overactive or underactive thyroid

• Can cause breathing and swallowing problems.

Other Disorders

• Addison’s disease

• Cushing’s syndrome

• Polycystic Ovary Syndrome (PCOS)

Which of the following glands use iodine to synthesise its hormones?

a.      Thyroid

b.      Pituitary

c.      Pancreas

d.      Hypothalamus

Learning Checkpoint 6

1.       In comparison to the nervous system describe the speed and mode of transport the endocrine system uses to transmit messages around the body.

2.       Identify the five major functions of the endocrine system.

3.       Define ‘hormone’.

4.       Briefly explain the mechanism in which hormones work their way around the body and find their way to different organs.

5.       Briefly explain the process of ‘negative feedback’ and comment on how it works within the endocrine system.

Systems in Sync

Urinary System

Overview & Main Functions

The urinary (renal) system works to purify internal body fluids and maintain fluid homeostasis. Every day it filters 150–180 L of fluid from the bloodstream, processing it to remove wastes and excess ions while returning needed substances to the blood. Bladders can vary in size causing individuals to need to go to the toilet more often.

Organs involved in the urinary system: Kidneys, ureter, urinary bladder

Key Functions

• Fluid homeostasis: Filters blood, removes wastes, returns needed substances.

• Excretion: Major system for removing metabolic wastes (lungs & skin help but cannot compensate if kidneys fail).

• Kidneys secret the following hormones:

  • Erythropoietin: Stimulates red blood cell production.

  • Renin: Helps regulate normal blood pressure, to increase blood pressure.

• Urine production & elimination: Via kidneys, ureters, bladder, urethra.

Kidneys Structure

• Bean‑shaped, dark red organs.

• Outer fibrous capsule, the cortex, innermost medulla with renal pyramids, functional unit is nephrons.

• Located between the 12th thoracic vertebrae, protected by lower ribs. In between spine, inferior to the diaphragm.

• They are found posteriorly to the abdominal wall.

• Right kidney lower than left due to liver.

• Held in place by renal fascia; surrounded by renal capsule.

• Kidneys are held in place by connective tissue

• An average adult kidney is approximately, 12 cm long, 6 cm wide, 3 cm thick.

Function

• Primary organs of the urinary system.

• Eliminate wastes, toxins, drugs by producing urine.

• Receive ¼ of total blood supply every minute due to constant filtration.

Urine dipsticks are thin plastic strips with chemical patches used to rapidly screen urine samples (within 60–120 seconds) for indicators of disease, such as infections, kidney damage, or diabetes. They test for pH, protein, glucose, ketones, bilirubin, blood, and leukocytes, providing quick, actionable diagnostic data.

Nephrons & Urine Formation

Each kidney contains over 1 million nephrons the structural and functional units.

·         The nephron is the basic structure of the kidney

·         A nephron is used to separate water ions and small molecules from the blood, filter out wastes and toxins and then return needed molecules to the blood.

·         Nephron functions through ultrafiltration

·         The ultrafiltration travels through various loops of the nephron, where water and important molecules are removed and into a collecting duct which drains into the bladder.

Nephron Structure

·         The nephron is a tubule that one end is closed and joined to a collecting duct the glomerular capsule (Bowman’s Capsule)

·         The glomerular capsule directly encloses the tiny arterial capillary network the glomerulus.

3 parts

-          Proximal convoluted tubule

-          Medullary loop (loop of Henle)

-          Distal convoluted tubule

Filtration takes place in the Glomerulus

Parathyroid Hormone – calcium and phosphate. This hormone raises the levels of calcium. Calcitonin reduces it.

Antidiuretic Hormone (ADH) – Increases reabsorption of water, controlled by a negative biofeedback mechanism

Aldosterone – increases reabsorption of water and sodium, increases the excretion of potassium, secretion is controlled by a negative feedback mechanism.

Atrial Natriuretic Peptide (ANP) – Decreases reabsorption of water and sodium and also controlled by a negative feedback mechanism.

Glomerulus – tiny ball shaped structure composed of capillary blood vessels actively involved in the filtration of the blood to form urine. The glomerulus is one key structure that makes up the nephron, the functional unit of the kidney.

Three Processes of Urine Formation

1.       Glomerular Filtration

·         the process in which water and solutes such as hormones, biochemical, ions and wastes are forced through the capillary walls of the glomerular capsule.

·         Once in the capsule the fluid is called filtrate and it is essentially blood plasma without protein.

2.       Tubular Reabsorption

·         Besides wastes and excess ions that must be removed from the blood, the filtrate contains many important substances such as: Water, Glucose, Ions

·         These substances are transported out of the tubule cells and removed from the filtrate.

·         Substances such as uric acid and urea remain in the filtrate.

3.       Tubular Secretion

·         Hydrogen, potassium, creatinine and other waste is removed from the blood and secreted by the tubule cells to be eliminated in the urine.

·         This process is of importance as it will remove substances that are not already in the filtrate – such as excess potassium and certain drugs.

Characteristics of Urine

·         The Colour of urine is due to the excretion of bile pigments.

·         Ph Normal range is 4.5 to 8

• 150–180 L of filtrate produced daily.

an average adult will excrete 1 to 1.5 litters a day 96% water, 2% urea, 2% uric acid, creatinine, ammonia, sodium and potassium ions, 2% phosphates, chloride, sulphates and oxalates.

• Filtrate ≠ urine:

  • Filtrate contains nutrients & ions.

  • Urine contains nitrogenous wastes, excess ions, unneeded substances.

• By the time filtrate reaches collecting ducts, most water & nutrients have been reabsorbed

• Some types of medications, vitamins and foods can change the colour or smell of your urine.

Angiotensin

§  The liver creates and releases a protein called angiotensinogen. This is then broken up by renin, an enzyme produced in the kidney, to form angiotensin I. This form of the hormone is not known to have any biological function in itself but is an important precursor for angiotensin II. As it passes in the bloodstream through the lungs and kidneys, it is further metabolized to produce angiotensin II by the action of angiotensin-converting enzyme.

§  The overall effect of angiotensin II is to increase blood pressure, body water and sodium content. Angiotensin II has effects on:

§  Blood vessels – it increases blood pressure by causing constriction (narrowing) of the blood vessels
 

§  Nerves: it increases the sensation of thirst, the desire for salt, encourages the release of other hormones that are involved in fluid retention.
 

§  Adrenal glands: it stimulates production of the hormone aldosterone, resulting in the body retaining sodium and losing potassium from the kidneys.
 

§  The kidneys: they increase sodium retention and alter the way the kidneys filter blood. This increases water reabsorption in the kidney to increase blood volume and blood pressure. 

Angiotensin 2

§  Angiotensin 2 acts as a vasoconstrictor, which raises blood pressure.

§  Renin and increased BP stimulate the release of aldosterone.

§  Water & sodium are reabsorbed, raising circulating blood volume

§  The increase in blood volume reduces the secretion of renin

Ureters

• Two slim tubes, 25–30 cm long.

• Carry urine from kidneys → bladder.

• Smooth muscle = layers their walls, contractions propel urine.

• Valve‑like folds prevent backflow into ureters.

S layer

§  Fibrous outer layer

§  Middle layer of smooth muscle

§  Inner layer of mucosa

Urinary Bladder

• Stores urine

• Collapsible muscular sac for temporary urine storage.

• Located behind the pelvis.

• Expands as urine accumulates without increasing internal pressure.

• When full: firm, pear‑shaped, palpable in lower abdomen.

3 layers

1.      Outer layer of loose connective tissue, containing blood and lymph vessels

2.      Middle layer interlacing smooth muscle and elastic tissue. Called the detrusor muscle, contacts to empty the bladder.

3.      Inner mucosa of traditional epithelium which allows the bladder to expand when needed.

Urethra

Thin-walled tube carrying urine from bladder to outside.

Sphincters

• Internal urethral sphincter: involuntary, keeps urethra closed.

• External urethral sphincter: voluntary, skeletal muscle, located in pelvic floor.

Female Urethra

• 3–4 cm long

• Opens near vaginal opening.

Male Urethra

• ~20 cm long

• Carries urine and semen

• Three regions:

  • Prostatic urethra (through prostate)

  • Membranous urethra (short section entering penis)

  • Spongy urethra (longest; runs entire penis length)

Disorders of the Urinary System

1. Urinary Tract Infection (UTI)

• Caused by bacteria entering urinary tract.

• Can affect urethra, bladder, or kidneys.

• More common in women.

• Symptoms: pain, fever, burning when urinating, blood in urine (haematuria).

• Treated with antibiotics.

2. Incontinence

• Loss of bladder control.

• Often due to weak pelvic floor muscles (common after childbirth).

• Can occur during physical activity or sneezing.

3. Kidney Stones

• Solid clumps of calcium forming anywhere in urinary tract.

• Caused by concentrated chemicals in urine.

• Symptoms: back/side pain, fever, blood in urine (Haematuria).

• Treated with medication; severe cases require surgery.

4. Kidney Failure (Renal Failure)

• Temporary or chronic inability to filter blood.

• Often caused by diabetes or hypertension.

• Leads to buildup of wastes in blood.

• Generally, ends up on dialysis treatments

Identify the function of the renal pelvis?

The renal pelvis stores urine before sending it down the ureters to the bladder.

Medical Terminology for Urinary System

Nocturnal Enuresis = involuntary bed wetting at night

Nocturia = excessive urination at night

Describe the process of urine formation: 6 Marks

Glomerular filtration occurs at the glomerulus, process which small molecules such as hormones, sugars, salts and amino acids pass through the semi-permeable capillary walls. Red blood cells and platelets should not pass through. Made up of filtrate and blood plasma without proteins. Tubular reabsorption occurs at the proximal convoluted tubule. Substances which are needed by the blood are reabsorbed based on the body’s needs. These include sugars, salts and amino acids which are selectively reabsorbed. Tubular Secretion occurs at the distal convoluted tubule. Hydrogen ions, and other unneeded substances e.g. drugs, potassium are secreted into the urine before it is excreted from the body.

Learning Checkpoint 8

1.      Describe the function of the urinary system. Function of the urinary system: It removes waste products and excess substances from the blood, regulates blood volume and pressure, controls levels of electrolytes and metabolites, and helps maintain acid-base balance and fluid homeostasis.

2.      Outline the process of ‘fluid homeostasis’. The process involves maintaining the balance of water intake and output to keep body fluids stable. The kidneys regulate fluid volume by filtering blood, reabsorbing needed water, and excreting excess as urine.

3.      Identify the other body systems that perform a similar function to the urinary system. The integumentary system (through sweating), respiratory system (through exhalation of water vapor and CO2), and digestive system (through elimination of waste in feces) also help remove waste and regulate fluid balance.

4.      Identify the structure responsible for urine formation. Structure responsible for urine formation: The nephron, located in the kidneys, is the microscopic functional unit that filters blood and forms urine.

5.      Describe the difference between the male and female urethra. Difference between male and female urethra: The male urethra is longer (approximately 20 cm), serving both urinary and reproductive functions by transporting urine and semen. The female urethra is shorter (about 4 cm) and only serves to transport urine.

6.      Identify the structures of the urethra that allows us to have conscious control over when we urinate. Structures allowing conscious control over urination: The external urethral sphincter, a voluntary muscle, allows conscious control over when urine is released. The internal urethral sphincter provides involuntary control.

7.      Describe how the urinary system interacts with the following body systems:

·         Cardiovascular system -   It filters the blood pumped by the heart, regulates blood pressure via fluid volume and secretion of hormones like renin.

·          Lymphatic system - Supports fluid balance and immune defence; the urinary system helps filter waste from bloodstream which includes lymph-filtered components.

·         Nervous system - Controls bladder storage and release through autonomic and somatic nerves for coordinated urination.

·         Endocrine system - Releases hormones (e.g., antidiuretic hormone from the pituitary, aldosterone from adrenal glands) that regulate kidney function and fluid balance.

Systems In Sync

Reproductive System

The primary function of the human reproductive system is to enable reproduction, ensuring the continuation of the species. Unlike other body systems that operate continuously, the reproductive system begins functioning at puberty. Its four main functions are:

• Production of egg and sperm cells (gametes)

• Transport and protection of these reproductive cells

• Support and nurturing of developing offspring during pregnancy

• Production of hormones that regulate reproduction and sexual behaviour

The system is divided into primary reproductive organs (gonads) and accessory reproductive organs. The gonads produce gametes and hormones, while accessory organs aid in transport, protection, and support of reproductive cells and offspring.

Male Reproductive System

Primary Organs

The testes are the male primary reproductive organs, responsible for producing sperm and the hormone testosterone. The testes are plum-shaped, approximately 4 cm long and 2.5 cm wide, and contain seminiferous tubules where sperm production (spermatogenesis) takes place. This process begins at puberty and continues throughout adulthood.

Duct System and Accessory Organs

·         Epididymis: A long, coiled tube on the surface of each testis that stores and matures sperm. During sexual stimulation, muscular contractions push sperm into the ductus deferens.

·         Ductus (Vas) Deferens: A muscular tube that propels sperm from the epididymis through the pelvic cavity, arching over the bladder to join the ejaculatory duct. Stores sperm and propels them forward the urethra during ejaculatory. Cutting of the ductus (Vas) deferens to prevent fertilization is called vasectomy.

·         Urethra: Extends from the bladder through the penis, serving as a stream for urine and semen. During ejaculation, the internal bladder sphincter constricts to prevent urine from mixing with semen.

·         Seminal Vesicles: Located at the bladder base, these glands produce seminal fluid, their ducts merge with those of the ductus deferens. Energy and Alkaline. Vesicles secrete an alkaline, viscous fluid that constitutes about 60% of the volume semen and contributes to sperm motility and viability.

·        

Prostate Gland: A small gland below the bladder that secretes a milky fluid aiding sperm activation. The prostate gland secretes a slightly acidic fluid that constitutes about 13-33% of the volume of semen and contributes to sperm mobility and viability. Lies in the pelvic cavity in front of the rectum. Completely surrounds the urethra. It also contains a clotting enzyme that allows semen to thicken when it enters the vagina, so it can survive until it reaches the cervix. The prostate can often enlarge as shown in the diagram.

·         Scrotum:  A sac of skin holding the testes and epididymis outside the abdominal cavity. Each sac contains a single testis, an epididymis and a spermatic cord. Scrotum also assists in regulating temperature critical for sperm development. Temperature is regulated with the cremaster muscle.

·         Penis: Contains erectile tissue that fills with blood during sexual excitement, enabling delivery of sperm into the female reproductive tract. It consists of a shaft terminating in the glans penis.

·         Testicles: spermatozoa are made in the seminiferous tubules in the testes. The testes, or testicles are paired oval shaped glands (gonads) in the scrotum. 3 layers.

1.       Tunica Vaginalis – a double membrane that is the outer cover of the testes.

2.      Tunica Albuginea – Fibrous covering the outer layer

3.      Tunica Vasculosa – inner most layer. Divides the testes into lobes.

Female Reproductive System

Primary Organs

The ovaries are the primary female reproductive organs, almond-shaped (about 3.5 cm long), and perform dual functions: producing eggs (ova) and hormones, primarily oestrogen and progesterone. Oestrogen is really important for regulating the menstrual cycle, and bone health. During menopause and perimenopause there is a decrease of oestrogen declining the overall bone health.

Within the ovaries, ovarian follicles contain immature eggs (oocytes). The follicle enlarges as the egg matures, culminating in ovulation, the release of a mature egg from the ovaries into the fallopian tube. Occurs 2 weeks before a period begins. During ovulation this is the prime time to get pregnant.

Duct System and Accessory Organs

Fallopian Tubes: Approximately 10 cm long, these tubes transport the mature egg from the ovaries to the uterus. The distal end has fimbriae - finger-like projections creating currents to draw the egg into the tube for potential fertilization.

• Uterus: A muscular, hollow organ located between the bladder and rectum, responsible for nurturing a fertilized egg. The uterus enlarges during pregnancy and contains a narrow outlet called the cervix, which dilates during childbirth to allow the baby to pass.

• Vagina: An 8–10 cm long thin-walled tube between the bladder and rectum, acting as the birth canal and exit route for menstrual blood.

External Genitalia (Vulva)

• Labia Majora and Labia Minora: Protective skin folds surrounding vaginal and urethral openings.

Clitoris: An erectile organ analogous to the male penis that responds to sexual stimulation.

• Mons Pubis: Fatty tissue located over the pubic bone providing protection.

Hormonal Role in Reproduction

Both males and females have gonadal hormones critical for development, function, and sexual behaviour:

• In Males: Testosterone regulates spermatogenesis, development of male secondary sexual characteristics, and libido.

• In Females: Oestrogen and progesterone regulate the menstrual cycle, development of female secondary sexual characteristics, and preparation of the uterus for pregnancy.

Common Reproductive Disorders

Female Reproductive Disorders

·        

Endometriosis: A condition in which the uterine lining tissue spreads outside the uterus into the abdominal cavity, causing symptoms such as abdominal pain, irregular periods, painful intercourse, and painful bowel or urinary functions.

·         Ovarian Cysts: Fluid-filled sacs on ovaries, common in women aged 30 to 45. While typically benign, some cysts can become cancerous, especially after age 40. Symptoms include abdominal pain, irregular menstruation, and pain during intercourse.

Male Reproductive Disorders

·         Testicular / Prostate Cancer: A common cancer in males aged 20 to 40, usually affecting one testis. It arises from sperm-producing cells and is highly curable if detected early. If untreated, cancer may spread to lymph nodes and other body parts, becoming fatal.

·         Benign Prostatic Hyperplasia (BPH) – Age associated prostate gland enlargement that can cause difficulty with urination. With this condition the stream of urine maybe weak or stop and start. It can lead to It can lead to infection, bladder stones and reduced kidney function.

·         Varicocele - An enlargement of the veins in the scrotum. Also called scrotum varicose veins. A varicocele may occur because of poorly functioning valves that are normally found in the veins. It may also occur from compression of a vein by a nearby structure. Varicoceles often produce no symptoms but can cause low sperm and decreased sperm quality, leading to infertility.

Systems In Sync

Learning Checkpoint 9

1.      Outline the four major functions of the reproductive system.

Production of gametes (sperm in males, eggs in females) for reproduction. Production of sex hormones (such as testosterone, estrogen, and progesterone) to regulate reproductive processes. Facilitation of fertilization where sperm and egg unite. Support of fetal development and childbirth (in females).

2.      Describe the structure, function and location of the following primary sex organs:

·         Testes:  Located in the scrotum outside the body. Their function is to produce sperm and male sex hormones (mainly testosterone).

·         Ovaries: Located on either side of the uterus in the female pelvic cavity. Their function is to produce ova (eggs) and female sex hormones (estrogen and progesterone).

3.      What is ‘ovulation’ and its role in reproduction?

Ovulation is the release of a mature egg (ovum) from an ovary, typically around the middle of the menstrual cycle. Its role in reproduction is to make the egg available for fertilization by sperm, enabling conception.

Integumentary System

Overview of the Integumentary System

The integumentary system is the body's largest organ system, primarily comprised of the skin and its accessory structures. It serves as a protective barrier, regulates physiological processes, and contributes to sensory perception. Skin is our first line of defence.

Function of the skin

1.      Protection - the skin protects the human body. When the skin is intact it acts as first line of defence against the invasion by micro-organisms, the skin also does the following: protects against dehydration, ultraviolet light, mild trauma and chemicals

2.      Synthesizes Vitamin D = 7-Dehyrocholesterol is a lipid substance in the skin converted to Vitamin D in sunlight. Ultraviolet radiation from the sun activates a precursor molecule, that starts to synthesis of vitamin D.

3.      Regulates and maintains body temperature = Sweat production is decreased in response to cold. Sweat is evaporated from the skin during exercise or high environmental temperature, helping to lower the body’s temperature to its normal range. The blood flow also changes in response to heat. When the body is hot the blood vessels dilate and the blood flows towards the surface of the skin to release heat. When cold the blood vessels constrict and the blood flows away from the skin’s surface to keep the body warm.

4.      Sensation = The skin is an organ of sensation. The skin has hundreds of nerve endings and receptors, detecting certain stimuli that are related to the sensations of pain, pressure, temperature and touch. (nerve ending receptors).

5.      Absorption = Limited absorption of drugs, (e.g – HRT and Nicotine patches). Some toxic chemicals can also be absorbed via the skin. Mercury is an example of this.

6.      Excretion = Then skin gets rid of waste products from the body including organic compounds, sweat, heat, water, salt – sodium chloride, urea and other spices.

Skin Anatomy

Epidermis

The epidermis is the outermost layer of the skin, composed mainly of keratinized stratified squamous epithelial cells. It serves as the primary barrier against environmental insults. Contains no blood vessels or nerve endings, no hair. Keratin cells within the epidermis produce keratin.  Melanocytes produce more melanin which results in a skin tan. Skin regenerates every 25 to 45 days.

• Layers of the epidermis (from superficial to deep):

  1. Stratum corneum: Composed of dead, flattened keratinocytes (corneocytes) embedded in a lipid matrix, providing a waterproof barrier.

  2. Stratum lucidum: Thin, translucent layer found only in thick skin (palms, soles).

  3. Stratum granulosum: Cells begin keratinization, containing keratohyalin granules.

  4. Stratum spinosum: Several layers of keratinocytes with desmosome connections providing mechanical strength.

  5. Stratum Basale (germinativum): Single layer of proliferative basal cells attached to the basement membrane; source of new keratinocytes.

• Cell types:

-          Keratinocytes (predominant) – to protect and waterproof the skin

-          Melanocytes (produce melanin pigment) – produces colour of the skin, absorbs UV Light.

-          Langerhans cells (immune surveillance) – Defence, comes from bone marrow and they migrate to epidermis. Interact with the T-helper cells, a type of white blood cell.

-          Merkel cells (sensory reception) – Located in the deepest layer of the epidermis, skin is hairless function with the sensation of touch.

• Structure-function relationship: The stratified arrangement and keratinization process create a tough, waterproof barrier that protects from pathogens, mechanical injury, and water loss.

Dermis

The dermis is a strong and stretchy layer of skin that helps hold the body together.  inner connective tissue layer beneath the epidermis. It supports and nourishes the epidermis and houses many accessory structures.

• Layers of the dermis:

  1. Papillary layer: Superficial with loose connective tissue; contains dermal papillae that interdigitate with the epidermis to increase surface area for nutrient exchange and strengthen attachment.

  2. Reticular layer: Deeper, thicker layer of dense irregular connective tissue; provides tensile strength and elasticity.

• Components: Collagen and elastin fibres, blood vessels, lymphatic vessels, nerve endings, sweat glands, sebaceous glands, hair follicles, Arrector Pili Muscles- smooth voluntary associated with hair.

• Function: Provides structural support, thermoregulation via blood flow, sensory input, and immune defence.

• Structure-function relationship: Rich collagen matrix resists mechanical stress; vascularization facilitates temperature and nutrient regulation.

Hypodermis (Subcutaneous Layer)

The hypodermis lies beneath the dermis and connects the skin to underlying tissues such as muscles and bones.

• Composition: Loose connective tissue with abundant adipocytes (fat cells) and larger blood vessels.

• Function: Provides cushioning, energy storage (lipids), insulation against heat loss, and anchors skin to underlying structures.

• Structure-function relationship: Fat pads absorb mechanical shock; vascular network supports skin and systemic circulation.

Accessory Structures of the Skin

Oil and sweat glands, hair and nails

Sweat Glands (Sudoriferous Glands)           

2.5 million sweat glands all over the body. Glands produce sweat, a clear fluid that is mostly water plus some salts, vitamins, wastes (urea) and lactic acid. Internal and external temperature changes in the body. Sudoriferous glands produce perspiration (sweat) which assists in the maintaining of body temperature and carry small amounts of wastes to the surface.

• 2 Types:

  1. Eccrine glands: Widely distributed, open directly onto skin surface. Produce watery sweat for thermoregulation via evaporation. Secrete sweat through the pores in the skin which is highly effective for heat regulating mechanisms.  Mostly found in the soles of the feet and the palm of the hands. Stimulated by an increase in temperature and emotions.

2.      Apocrine glands: Found in genital areas of the body and also axilla and pubis and are larger than eccrine glands. Their ducts empty into hair follicles and contain fatty acids, proteins and the substances secreted by the eccrine glands. Apocrine glands begin to function during puberty and play a minimal role in regulating body temperature.

• Structure: Coiled tubular glands originating in the dermis or hypodermis.

• Function: Regulate body temperature, excrete waste products, and in apocrine glands, may have roles in pheromone communication.

• Physiological process: Sweat production is stimulated by sympathetic nervous system; evaporation of sweat dissipates heat.

Sebaceous Glands (Oil Glands)        

• These are simple glands that produce oil and waxes. They are found in various places on the body including the skin, scalp, groin, face and axillae. They are secretory epithelial cells.

• Sebaceous (oil) glands are usually connected to the hair follicles; they are absent in the palms and soles.

• Sebaceous glands produce sebum, which moistens hairs, waterproofs and softens the skin.

• Act as a fungicidal and bactericidal agent preventing many infections.

• Help to keep the moist and from drying out.

• Enlarged sebaceous glands may produce blackheads, pimples and boils.

Hair

• Hairs, also known as pili. Keratin filaments with a root and shaft with an arrector pili muscles.

• The arrector pili muscle is a bundle of smooth muscle fibers that are attached to each hair follicle.

• When the arrectores pilorum contract they raise the skin and cause the hair to stand upright. This reaction is called goose bumps. This occurs when a person is called or has a fight.

• Hair assists in thermoregulation. Provides limited protection against injury. Hair protects the scalp – from UV light.

• Nasal hairs = protect the nostrils from inhalation of foreign matter and insects.

• Eyelashes and eyebrows = protect the eyes from the entrance of foreign matter.

Nails

• Nails are found overlying the epidermis of the tops of the fingers and toes and underneath a fold of skin.

• Nails are made of heavily keratinized epidermal cells.

• The principal parts of a nail are the body, free edge, root, lunula, eponychium and matrix.

• Cell division of the matrix produces new nails.

• Functionally nails = help in grasping and manipulating small objects.

• Provide protection against trauma of the ends of the digits. Allow us to scratch.

Common Skin Disorders

Acne

• Cause: Blockage and inflammation of sebaceous glands and hair follicles.

• Mechanism: Excess sebum production, keratin buildup, bacterial colonization (e.g., Propionibacterium acnes), and inflammation.

• Symptoms: Pimples, blackheads, cysts, and potential scarring.

Dermatitis

• Description: Broad term for skin inflammation due to irritants or allergens.

• Types: Contact dermatitis (irritant or allergic), atopic dermatitis.

• Symptoms: Redness, itching, swelling, vesicles, scaling.

Eczema

• Definition: Chronic inflammatory condition marked by dry, itchy, and inflamed skin.
  Often linked to genetic predisposition and immune dysfunction.

• Pathophysiology: Barrier dysfunction causing increased water loss and allergen penetration.

Psoriasis

• Cause: Autoimmune disorder characterized by accelerated epidermal cell proliferation.

• Features: Thickened, scaly, silvery plaques, often on extensor surfaces.

• Mechanism: T-cell mediated inflammation leads to hyperproliferation of keratinocytes.

Hives (Urticaria)

• Cause: Hypersensitivity reaction causes histamine release, increasing vascular permeability.

• Symptoms: Raised, itchy welts that vary in size and location.

• Triggers: Allergens, stress, infections, medications.

Skin Cancer

• Types:

  1. Basal cell carcinoma: Most common, arises from basal layer keratinocytes; slow-growing and rarely metastatic.

  2. Squamous cell carcinoma: Originates from keratinocytes in upper epidermis; potential for metastasis.

  3. Melanoma: Malignant tumour of melanocytes; highly aggressive and metastatic.

• Risk factors: UV exposure, fair skin, genetic predisposition.

• Prevention: Sun protection, early detection and removal.

Learning Checkpoint 10

1.       Describe the major functions of the integumentary system.

·         Protection against environmental hazards (pathogens, chemicals, physical injury).

·         Regulation of body temperature through sweating and blood flow.

·         Sensation through nerve receptors for touch, pain, and temperature.

·         Prevention of water loss and dehydration.

·         Production of vitamin D when exposed to sunlight.

·         Excretion of waste products through sweat.

·         Immune defence via specialized cells in the skin.

3.      Describe the structure of skin

Epidermis: Outer layer made of stratified squamous epithelial cells that provides a waterproof barrier. Dermis: Middle layer containing connective tissue, blood vessels, nerves, hair follicles, and glands. Hypodermis (subcutaneous layer): Inner layer of fat and connective tissue that cushions and insulates the body.

4.      Identify the layer of skin that is constantly shedding cells.

The epidermis's outermost layer, the stratum corneum, is continually shedding dead skin cells.

5.      Identify the time taken for a new layer of skin to be produced.

It typically takes about 4 to 6 weeks for new skin cells to be produced in the epidermis and reach the surface to replace shed cells.

6.      Identify the accessory structures of the integumentary system

·         Sweat glands: Produce sweat for temperature regulation.

• Sebaceous (oil) glands: Secrete oils that lubricate and waterproof skin.

• Hair follicles and hair: Provide protection and sensory input.

• Nails: Protect the tips of fingers and toes and assist with manipulation.

Systems In Sync

Nervous System

Main Functions of the Nervous System

The nervous system serves as the body’s primary controlling, regulating, and communication network. It governs all mental activities, including thought, learning, and memory, through rapid electrical impulses that evoke immediate responses. The nervous system performs three interrelated functions:

1. Monitoring stimuli: It detects changes inside and outside the body using millions of sensory receptors, gathering sensory input.

2. Integration: It processes and interprets sensory input to determine appropriate responses.

3. Motor output: It activates muscles or glands (effectors) to produce a response.

For example, seeing a red traffic light (sensory input) leads the brain and spinal cord to integrate this information and send motor commands to apply the brake, producing the physical response.

Structural Classification: Central and Peripheral Nervous Systems

Central Nervous System (CNS)

The CNS consists of the brain and spinal cord, which act as command centres. It interprets sensory information and issues instructions to the body.

Peripheral Nervous System (PNS)

The PNS consists of all nerves outside the CNS, including cranial and spinal nerves. It connects the CNS to body organs, muscles, and glands. The PNS is subdivided into:

• Afferent (sensory) division: Transmits impulses from sensory receptors to the CNS.

• Efferent (motor) division: Carries impulses from the CNS to effectors; further subdivided into:

  • Somatic nervous system: Controls voluntary skeletal muscle movements (including involuntary reflexes).

  • Autonomic nervous system (ANS): Regulates involuntary actions in cardiac muscle, smooth muscle, and glands, comprising:

    • Sympathetic division: “Fight-or-flight” responses for stressful situations.

    • Parasympathetic division: “Rest-and-digest” responses for calm states.

Neurons are classified by function into:

• Sensory (afferent) neurons: Carry impulses from sensory receptors to the CNS; detect pain, stretch, and other sensations.

• Motor (efferent) neurons: Transmit impulses from the CNS to muscles and glands.

• Interneurons: Connect sensory and motor neurons and facilitate communication within the CNS.

Divisions Of the Nervous System

Photo on phone write information

Major Brain Regions and Their Functions

Spinal Cord Structure and Protection

The spinal cord is a cylindrical extension of the brainstem approximately 42 cm long, protected by the vertebral column. It acts as a two-way communication pathway between the brain and the body and serves as a major reflex centre.

The spinal cord features:

• Grey matter: Shapes like a butterfly; contains dorsal (posterior) grey horns and ventral (anterior) grey horns surrounding the central canal filled with cerebrospinal fluid (CSF).

• White matter: Composed of myelinated fibre tracts (dorsal, lateral, and ventral columns) that transmit sensory (to brain) and motor (from brain) impulses.

Protection is provided by:

• Bone: The vertebral column encases the spinal cord.

• Meninges: Three connective tissue layers dura mater (outer), arachnoid (middle), and pia mater (inner) protect and cushion the CNS. Inflammation of tissue = Meningitis

• Cerebrospinal fluid (CSF): A watery fluid that cushions nervous tissue, circulates through brain ventricles and spinal canal, and is produced by the choroid plexus.

• Blood-brain barrier: Protective capillary system that restricts harmful substances in the blood from reaching the brain, allowing only essential molecules like glucose, water amino acids and drugs.

Reflex Mechanisms

Reflexes are rapid, involuntary, and predictable responses to stimuli that occur via reflex arcs involving both CNS and PNS. Reflexes are classified as:

• Somatic reflexes: Involve stimulation of skeletal muscles, such as quickly withdrawing a hand from a hot object.

• Autonomic reflexes: Regulate smooth muscle and gland activity, controlling functions like heart rate, digestion, blood pressure, and sweating.

Common Disorders of the Nervous System

Epilepsy

An episodic disorder characterized by sudden, excessive electrical discharges in brain neurons ("electrical storms"), causing seizures. Causes include genetics, brain injury or infection, stroke, and brain abnormalities.

Meningitis

An infection of the protective membranes (meninges) surrounding the brain and spinal cord. Caused by bacteria or viruses and preventable by immunization. Symptoms in infants and children include fever, difficulty waking, purple-red rash or bruising, and loss of appetite. Untreated meningitis can be fatal.

Multiple Sclerosis (MS)

A chronic autoimmune disease where the immune system attacks myelin sheaths covering nerve fibres in the CNS, disrupting electrical signalling. This results in symptoms such as fatigue, bladder and bowel dysfunction, mood changes, sensory disturbances (tingling, numbness), and visual problems. MS primarily affects young adults, with a higher prevalence in women.

Learning Checkpoint 11

1.       Describe the interrelated functions of the nervous system.

The nervous system performs sensory input, integration and motor output. Sensory neurons detect stimuli and send information to the CNS, the CNS interprets this information, and then motor neurons carry signals to effectors to produce a response.

2.       Identify the two structural classifications of the nervous system and identify the organs within each.

The Central Nervous System (CNS) is made up of the brain and spinal cord. It is responsible for processing, integrating and coordinating all incoming sensory information and outgoing motor responses. The Peripheral Nervous System (PNS) is consists of all nerves outside the CNS, including cranial nerves, spinal nerves, and peripheral ganglia. It carries sensory information to the CNS and motor commands from the CNS to muscles, organs and glands. These two systems work together, the PNS detects and transmits information, while the CNS interprets and responds, forming one integrated communication network.

3.       Briefly outline the function of the PNS.

The Peripheral Nervous System (PNS) is consists of all nerves outside the CNS, including cranial nerves, spinal nerves, and peripheral ganglia. It carries sensory information to the CNS and motor commands from the CNS to muscles, organs and glands.

4.       Describe the difference between the afferent division and the efferent division of the PNS.

Afferent division are the signals going up towards the brain and the efferent division is going from the brain to the muscles.

5.       Explain the function of the somatic or voluntary nervous system.

6.       Explain the function of the automatic nervous system (ANS).

7.       Explain the function of the sympathetic nervous system.

8.       Explain the function of the parasympathetic system.

9.       Briefly outline the function of the CNS.

10.   Outline the structure and function of the spinal cord.

11.   Explain reflexes.

Systems In Sync

Lymphatic and Immune System

Functions

1.      Draining excess interstitial fluid – prevents oedema = Swelling

2.      Transporting dietary lipids (Fats) from the Gastrointestinal Tract (GIT) to the blood.

3.      Transporting lost plasma proteins back to the blood. Protecting the body against invasion through the immune response – (t-cells, B-cells).

4.      Drainage of tissues returns fluid that has escaped from blood circulation back into the blood stream and drain excess fluid away.

5.      Immunity: Produces mature lymphocytes in bone marrow

6.      Fat Absorption: lacteals in the bowel absorb fat- and fat-soluble materials.

Structure and Components of the Lymphatic System

The lymphatic system is an essential part of the body's defence and fluid regulation mechanisms. It comprises a complex network of vessels, organs, and tissues that work together to maintain fluid balance and support immune function.

• Lymphatic Vessels: These vessels transport lymph, a clear fluid containing white blood cells, throughout the body. They begin as blind-ended capillaries in tissues, collecting interstitial fluid, and progressively merge into larger vessels that return lymph to the bloodstream via the subclavian veins. Valves in the vessels ensure unidirectional flow.

• Lymph Nodes: Small, bean-shaped structures located along lymphatic vessels. The function of the lymphatic vessels is forming a drainage system that picks up excess tissue fluid called lymph and returns it to the blood. The lymphatic vessels form a one- way system that transports lymph towards the heart. Lymph capillaries are found between the tissue cells and blood capillaries in loose connective tissue in the body.

• Spleen: The largest lymphatic organ, the spleen filters blood, removes aged or damaged red blood cells, and serves as a reservoir for white blood cells and platelets. It also detects and responds to blood-borne pathogens.

• Thymus Gland: Located in the upper chest, the thymus is crucial for T-lymphocyte maturation. It provides an environment where precursor T cells develop immunocompetence before entering peripheral circulation.

• Bone Marrow: The primary site of haematopoiesis, bone marrow produces all blood cells, including immune cells such as B-lymphocytes, T-lymphocyte precursors, phagocytes, and others.

• Mucosa-Associated Lymphoid Tissue (MALT): Collections of lymphoid tissue found in mucous membranes lining the digestive, respiratory, and urogenital tracts. MALT includes structures like tonsils and Peyer's patches and plays a critical role in immune surveillance at body entry points.

• Tonsils: found in the mouth and throat and their function is to destroy inhaled pathogens.

Roles of the Lymphatic System in Fluid Balance and Immunity

The lymphatic system performs two pivotal roles:

1.       Fluid Balance: It collects excess interstitial fluid that leaks from blood capillaries and returns it to the bloodstream, thus preventing tissue enema and maintaining blood volume and pressure.

2.       Immunity: By transporting lymph containing immune cells and filtering pathogens through lymph nodes, the lymphatic system acts as a frontline for detecting and responding to infections. It facilitates immune cell communication and antigen presentation necessary for initiating immune responses.

Distinction Between Innate and Adaptive Immunity

The immune system consists of two complementary arms:

• Innate Immunity: The body's first line of defence that provides rapid, nonspecific protection against pathogens. It includes physical barriers (skin, mucous membranes), chemical barriers (acidic secretions), and cellular defences such as phagocytes and natural killer cells.

• Adaptive Immunity: A highly specific, slower response that develops after exposure to a particular pathogen. Adaptive immunity involves the activation of lymphocytes (B and T cells), antigen recognition, and the production of memory cells that enable faster responses upon subsequent exposures.

Key Immune Cells and Their Functions

• Phagocytes: These cells, including macrophages and neutrophils, engulf and destroy pathogens and cellular debris through the process of phagocytosis. They are critical components of innate immunity and also act as antigen-presenting cells.

• Natural Killer (NK) Cells: A type of lymphocyte involved in innate immunity, NK cells can recognize and kill virus-infected cells or tumour cells without prior sensitization, using cytotoxic granules.

• B-Lymphocytes (B Cells): Central to adaptive immunity, B cells recognize specific antigens and differentiate into plasma cells that produce antibodies. Antibodies neutralize pathogens and mark them for destruction.

• T-Lymphocytes (T Cells): Also, part of adaptive immunity, T cells mature in the thymus and specialize into different subsets:

  • Helper T Cells: Assist other immune cells by releasing cytokines that modulate immune responses.

  • Cytotoxic T Cells: Destroy infected or abnormal cells by inducing apoptosis.

  • Regulatory T Cells: Maintain immune tolerance and prevent autoimmunity.

Processes of Antigen Recognition and Antibody Production

Antigen recognition is initiated when immune cells detect specific molecular structures (antigens) on pathogens or abnormal cells:

• Antigen Presentation: Phagocytes and other antigen-presenting cells process pathogens and display antigen fragments on their surface bound to major histocompatibility complex (MHC) molecules to activate T cells.

• Activation of Lymphocytes: Helper T cells recognize presented antigens and stimulate B cells and cytotoxic T cells. B cells bind antigen directly through their receptors.

• Antibody Production: Activated B cells differentiate into plasma cells that secrete antibodies specific to the antigen. Antibodies neutralize pathogens, facilitate phagocytosis (opsonization), and activate the complement system to destroy infected cells.

Inflammation and Fever as Immune Responses

• Inflammation: A localized response to infection or injury characterized by redness, heat, swelling, pain, and loss of function. It involves the release of chemical mediators (like histamine) that increase blood flow and capillary permeability to recruit immune cells to the affected area.

• Fever: A systemic elevation of body temperature triggered by pyrogens released by immune cells or pathogens. Fever enhances immune efficiency by accelerating the activity of immune cells and inhibiting pathogen replication.

Common Immune-Related Illnesses

• Glandular Fever (Infectious Mononucleosis): Caused by the Epstein-Barr virus, this illness affects lymphoid tissues, notably the lymph nodes and spleen. Symptoms include fever, sore throat, swollen lymph nodes, and fatigue due to an intense immune response involving lymphocyte proliferation.

• Crohn's Disease: A chronic inflammatory bowel disease characterized by an abnormal immune response against intestinal tissues. This results in inflammation, ulceration, and damage of the gastrointestinal tract due to dysregulated immune activation.