Human Endocrine System

Chemical coordination

• Is described as a slow, prolonged process of communicating information throughout the body

• The endocrine system is responsible for chemical coordination

• Endocrine glands release hormones

• The endocrine system works with the nervous system

Nervous system

Electrical impulses are the messengers in the nervous system

Endocrine system

Hormones are the chemical messengers in the endocrine system that target cells through the bloodstream

Hormone

an organic chemical substance (usually protein) which is used to carry information from one part of the body to another to regulate metabolic function

What does a hormone do?

Hormones are secreted by an endocrine gland, released into bodily fluids, like blood, which carry them to target cells

Target cells respond to a hormone when they express a specific receptor for that hormone

Properties of hormones

• Some are Proteins - insulin, thyroxine

• Some are Fats - Steroids - testosterone

• Powerful in small concentrations

• Very short life

• Can stimulate target cells to release another hormone

• Can have several special effects

• Do not operate in isolation but in conjunction with other hormones and the CNS

What is an endocrine gland?

A vascular (rich in flood easels), ductless gland that secretes hormones

Humans have nine endocrine glands

Endocrine vs Exocrine Gland

Homeostasis

the maintenance of a relatively constant internal environment despite changes in the external environment of the organism

For cells, and therefore the body, to function properly, the internal environment needs to stay stable in terms of temperature, water concentration, electrolytes, CO2 and oxygen, glucose and other solutes and pH

How is homeostasis maintained?

any changes that occur (deviations from the “ideal”), need to be detected and then changes need to be made to return the body to the “set norm” or ideal

The major mechanisms that allows for this detection and correction is call negative feedback.

Negative feedback

• operates if the system is disturbed

• It sets off a sequence of events which counteract (opposite or negative to) the disturbance and tends to restore the system to its original state

• Is therefore the mechanism by which animals maintain a constant state

Negative feedback loop

Variable (in homeostasis)

1. Stimulus: produces change in variable

Imbalance

2. Change detected by receptor

Receptor (sensor)

3. Input: Information sent along afferent pathway to

Control centre

4. Output: Information sent along efferent pathway to activate

Effector

5. Response of effector feeds back to influence magnitude of stimulus and returns variable to homeostasis

Hypothalamus

• Controls function of Pituitary gland

• Acts as the link between the nervous system and endocrine system

• Receives information from many parts of the brain - pain, illness, emotions, biological clock, stress, hormone levels, state of blood, appetite etc.

• Stimulates the secretion of the hormone ADH (anti-diuretic hormone) from the posterior pituitary gland

• ADH controls the amount of water absorbed into the blood by collecting tables in the kidneys

Diuretic

To pass urine/water

Anti-diuretic

To reduce the passing of urine/water

How does ADH control the amount of water in the blood?

1. Hypothalamus detects too much water in blood

2. Pituitary gland releases less ADH

3. Kidneys reduce blood water levels

4. So more water reaches the bladder (urine more dilute)

5. Blood water level returns to normal

The posterior pituitary (neurohypophysis)

Stores and secretes hormones produces by the hypothalamus

Pituitary gland (anterior)

Growth hormone/ S.T.H: Somatotropin hormone

• Promotes skeletal and muscular growth

Too little growth hormone in babies

Pituitary dwarfism. Underdevelopment of skeleton

Too much growth hormone in babies

Giant: Rare- normally caused by a tumour in the pituitary gland

Too much growth hormone in adults

Acromegaly. Enlarged hands, jaw bone and brows. Bones can only thicken as the growth plates are no longer active.

Hyposecretion of growth hormone / STH

• Underdevelopment of skeleton

• Caused by disease

• Height reduced but proportions are normal

• Not mentally retarded by may be sexually immature

• Can be treated by injections of synthetic growth hormone (STH) produced by genetically engineered bacteria

Anterior lobe (blood)

• Growth hormone

• TSH

• LH

• FSH

• Prolactin

Growth hormone

Promotes growth by stimulating protein synthesis

TSH (Thyroid Stimulating Hormone)

Stimulates the thyroid to produce thyroxin

LH (Luteinizing Hormone)

In females stimulates ovulation

In males stimulates the cells of Leydig to produce testosterone

FSH (Follicle Stimulating Hormone)

In females stimulates the formation of the primary follicle

In males activates epithelial cells to produce sperm cells

Prolactin

Stimulates mammary glands to produce milk after birth

Posterior lobe (nerves)

• ADH

• Oxytocin

ADH (Antidiuretic Hormone)

• Produced in the hypothalamus + stored in the posterior lobe

• When dehydrated the hypothalamus stimulates the posterior lobe to release ADH

• Function: Controls water reabsorption in the kidneys

Oxytocin

Produces in hypothalamus and released from posterior lobe

Positive feedback

Function: Causes contractions of the uterus during labour

1. Baby pushes against cervix, causing it to stretch

2. Stretching of cervix causes nerve impulses to be sent to brain

3. Brain stimulates posterior pituitary to release oxytocin

4. Oxytocin causes smooth muscle lining the uterus to contract

Thyroid

• Controls rate of cellular metabolism

• Involved in growth and development

Thyroid gland

Found below the larynx, across the trachea and in front of the neck

• Produces the hormone THYROXIN.

• THYROXIN controls metabolic rate. Metabolic rate is the rate at which cells can produce energy...therefore it can stimulate growth and development of organs.

• Thyroxin cannot be made without iodine.

• Thyroxin-stimulating hormone (TSH) released from the pituitary gland controls the production of thyroxin

• The production of thyroxin is controlled by TSH

Thyroxin

• Increase basal metabolic rate (energy body needs to function at rest)

• Increase breathing rate + heart rate

• Normal growth and development of your organs

• Essential for functioning of the nervous system

Disorders of the thyroid gland

• Hypothyroidism

• Hyperthyroidism

Hypothyroidism

Insufficient production of thyroxin

Cretinism

Hypothyroidism in children

Slow mental growth, slow bone growth (short), thick dry skin

Myxoedema

Hypothyroidism in adults

Thickened skin, tongue, mental and physical abilities slow down

Weight gain, coarse skin, mental and physical sluggishness

Hyperthyroidism

Excessive thyroxin production

Swollen thyroid gland: goitre, protruding eyes, weight loss, sweating, hand tremor, fast heart rate and hyperactivity

Graves’ disease

Loss of weight, hyperactive, nervous insomnia, increased BP, heart problems

Common cause of hyperthyroidism which causes enlargement of the thyroid and other symptoms such as exophthalmos, heat intolerance and anxiety

Exophthalmia

Protruding eyes

Goitre

Lack of iodine in the body, and thyroid gland becomes swollen

Thyroid - Negative feedback loop

Thyroid → more thyroxin → pituitary gland → more TSH → thyroid

Thyroid → less thyroxin → pituitary gland → less TSH → thyroid

Adrenal glands

Endocrine glands which secrete adrenaline and cortisol

Hormones which help regulate chemical balance, regulate metabolism and supplement other glands

Adrenal glands…

the cortex and the medulla secrete different hormones

Cortex

Secretes cortisol and aldosterone

Medulla

Secretes adrenalin

Adrenalin

Secreted during times of stress - fight or flight hormone

Effects of adrenaline on the body

• Accelerates heart rate

• Increases blood pressure

• Increases conversion of glycogen to glucose

• Increases breathing rate

• Increases muscle tone

• Dilates pupils

• Increases sweat production

Hormones of the adrenal cortex

1. Cortisone

2. Aldosterone

Cortisone

Increases body’s ability to resist stress of all kinds, it is anti-inflammatory and anti-allergic

Aldosterone

Regulates your ionic balance of tissue fluid

Causes increased reabsorption of sodium and chloride ions from filtrate it kidney. Therefore helps regulate electrolytes levels in body.

Fight or flight response

• Saliva flow decreases

• Eyes: pupils dilate

• Skin: blood vessels constrict : chills and sweating

• Lungs: quick, deep breathing occurs

• Heart beats faster and harder

• Stomach: output of digestive enzymes decreases

• Bowel: food movement slows down

• Blood vessels: blood pressure increases as major blood vessels dilate

• Muscles become more tense; trembling can occur

Cushing’s syndrome

Due to overactive adrenal glands from excessive production of cortisol

Thinning of hair, red cheeks, acne, moon face, buffalo hump, supraclavicular fat pad, increased body and facial hair, weight gain, purple striae, pendulous abdomen, ecchymosis resulting from easy bruising, thin extremities with muscle atrophy, thin skin and subcutaneous tissue, slow wound healing

How does stress affect the adrenal hormones? What is adrenal fatigue?

Watch the video lol

The Pancreas

• Both an exocrine and an endocrine gland

• The endocrine portion is made up of the islets of langerhans. The islet contains two types of cells: ALPHA and BETA cells

• The ALPHA cells produce GLUCAGON, while the BETA cells produce INSULIN

• INSULIN decreases blood glucose by; stimulating cells to take up and use glucose for energy; changes glucose to glycogen that is stored in the liver and muscles; changes excess glucose into fat which is stores in fat cells

• GLUCAGON increases blood glucose by; breaking down glycogen into glucose in the liver

Negative feedback loop - Pancreatic hormones

Insulin

• Glucose is absorbed from small intestine after a meal, blood passes through pancreas and beta cells detect raised blood glucose level so respond by secreting insulin

• The main target organs of insulin are the liver and muscles making cell membranes more permeable to glucose

• Insulin also increases the rate at which excess glucose not used immediately for energy is converted to glycogen

• Blood glucose levels are therefore lowered

• I.e. negative feedback control mechanism

Glucagon

• When glucose levels are low when waking up or after exercise the alpha cells in pancreas registers this and secretes glucagon

• Glucagon works on liver cells to breakdown of stored glycogen and converts it back to glucose

• Therefore glucose levels in the blood increase

Diabetes mellitus

Some people’s Islets of Langerhans do not produce insulin.

Deficiency of insulin or insulin resistance.

Disorders of the Pancreas

1. Type 1 (insulin-independent)

2. Type 2 (non-insulin dependent or insulin resistant)

Type 1: (Insulin-dependent)

• Develops suddenly before aged 15

• Insulin-secreting cells damaged (immune system damage/viral infection)

• Have to have an insulin injection everyday as body cannot use glucose in blood without it

• Some long term problems include: loss of feeling in skin, impaired bladder function, heart attacks, gangrene and blindness

Type 2: (non-insulin dependent or insulin resistant)

• Occurs after age 40 but can develop sooner

• Bodies produce insulin, but it is not enough OR target cells do not respond to insulin properly

• People suffering from type 2 diabetes are normally overweight

Type 1 diabetes

Occurs in children and young adults as a result of an autoimmune response leading to the deficiency or absence of insulin

Treated with …

Genetic engineering to produce insulin

…

Type 2 diabetes

• Most common form of diabetes and is usually a more gradual process

• Insulin resistance

• Mostly caused by poop lifestyle habits

Diabetic complications

• Retinopathy

• Glaucoma

• Elevated blood glucose responsible for blood vessel clogging and damage and elevated blood pressures (damaged kidneys, heart disease, atherosclerosis)

• Body ulcers and lack of circulation to extremities

• Nerve damage

Retinopathy

blood vessels distort in the retina and impair vision

Glaucoma

Build up of pressure in the eye

Control of blood sugar

• Monitoring of blood sugar levels

• Diet

• Pancreatic stimulants

• Insulin

• Exercise

• Weight control

• Lean body mass (muscle to fat ratio)

Glycemic Index foods

High GI, Medium GI, Low GI

The influence of glycemic index on the blood glucose level

Alpha cells → Glucagon

• Blood glucose decreases below normal

• Glucagon released

• Converts glycogen to glucose

• Glucose released from liver and muscles

• Blood glucose levels increase

Beta cells → Insulin

• Secreted when blood glucose levels increase

• Causes blood glucose levels to decrease

• Stimulates the conversion of glucose to glycogen

• Which is stored in the liver and muscles

Ovaries

Apart from producing and releasing gametes (eggs), the ovary produces and secretes:

• Oestrogen

• Progesterone

• (Also 1 quarter of her total testosterone)

Oestrogen

Responsible for:

• Rapid increase in physical growth during puberty

• Appearance of secondary sexual characteristics (breast, body hair)

• Maturation and maintenance of reproductive organs

• In conjunction with progesterone promotes cyclic changes in endometrium during ovulation/menstrual cycle and prepares uterus for pregnancy

• Sex drive, vaginal lubrication

Progesterone

Responsible for:

• (With oestrogen) promotes cyclic changes in endometrium

• During pregnancy helps maintain endometrium in a functional state

• During pregnancy helps keep uterus wall muscles relaxed

Testes

Apart from producing and releasing gametes (sperm), the testes produce and secrete:

• testosterone

Testosterone

Responsible for:

• rapid increase in physical growth during puberty

• Appearance of secondary sexual characteristics (body hair)

• Maturation and maintenance of reproductive organs

• Production of sperm

• Sex drive

Disorders of the gonads and their endocrine function

PCOS

Performance enhancing drugs in sport

Human growth hormone:

• More difficult to detect in drug tests

• Lack of scientific evidence that it improves performance, but sporting community believes it does

Anabolic steroids

• Testosterone and oestrogen

Erythropoietin

• increases red blood cell count → increases oxygen carrying capacity → increases performance