Biology - Unit 4: Homeostasis

Homeostasis

• ability for the body to maintain a relatively stable internal environment despite environmental changes

Sensor

• a body structure that detects a change in a variable and sends a signal to the control centre

Control Centre

• a body structure that sets a range of values for a variable

• receives signal from sensor

• sends signal to effectors

Effectors

• receives signal from control centre and responds, leading to a change in the variable

• the tissue/organ that carries out the actual response, not the hormone/gland

Feedback Systems

• used to regulate internal environment

Negative Feedback Loop

• the system (body) reverses a change to bring it back to a normal range; stabilization

• e.g. temperature regulation

Positive Feedback Loop

• the body (system) increases a change in a variable; amplification

• e.g. blood clotting, fruit ripening, childbirth

Set Point

• normal level of a variable

Beta Cells

• produces insulin to lower blood glucose levels

Alpha Cells

• produces glucagon to raise blood glucose levels

Insulin

• stimulates cells to absorb more glucose for respiration

• stimulates liver to store glucose as glycogen

• lowers blood glucose

Glucagon

• stimulates liver to break down glycogen to release glucose

• raises blood glucose

Type 1 Diabetes

• immune system produces antibodies that attack & destroy beta cells → no insulin

Type 2 Diabetes

• insulin receptors on cells stop responding to insulin or beta cells cannot produce enough insulin

Diabetes Symptoms

• increased thirst, urination, and hunger; numbness; tiredness; blurry vision

Growth

• physical changes to the body

Development

• the gaining of skills and abilities as humans age

Fight-or-Flight

• scared → adrenal glands release cortisol and adrenaline

• liver breaks down glycogen, digestion slows down, increased breathing and heart rate, sweating

Cushing’s Syndrome

• too much cortisol over a long period of time

• typically due to a tumour in the adrenal glands

• symptoms - weight gain with thin limbs, increased fat in neck, easy bruising, muscle weakness

Hashimoto’s Disease

• autoimmune, buildup of WBCs in thyroid → underactive thyroid → not enough thyroid hormones produced to regulate body

• symptoms - fatigue, dry skin, unexplained weight gain, muscle weakness

Endocrine System

• works with the nervous system to maintain homeostasis by releasing hormones

Hormones

• chemical messengers that regulate bodily functions

• produced by a secreting cell and only has an effect on target cells

• some hormones have multiple targets

• works slowly, has long lasting effects

Endocrine Glands

• structure that releases hormones directly into the bloodstream

• ductless, for distant targets

Exocrine Glands

• releases non-hormonal substances (e.g. sweat)

• has ducts, for local targets

Peptide Hormones

• most hormones; short chains of amino acids

• needs to bind to a receptor - cannot penetrate cell membrane (polar v. nonpolar)

• binds to receptor on surface of cell → triggers series of reactions inside the target cell

Steroid Hormones

• ring structure, no receptor needed

• binds to receptor protein in the cell → hormones activate genes → changes are made to the cell

Hypothalamus

• connects nervous and endocrine systems

• receives signals from various parts of the body → stimulates pituitary gland to release needed hormones

Pituitary Gland

• considered the “master gland” - releases hormones to many other glands to regulate various functions

• small pea-sized gland, has 2 lobes

Anterior Pituitary

• produces and releases the following: FSH, LH, ACTH, HGH

Posterior Pituitary

• makes and releases antidiuretics and oxytocin

Gonads

• organs that produce gametes (testes & ovaries)

Testes

• produces sperm & testosterone

• made of seminiferous tubules (sertoli & leydig cells)

Scrotum

• pouch of skin around the testes, regulates temperature of the testes

Penis

• transfers sperm to the female

Sertoli Cells

• stimulates spermatogenesis and provides nutrients for sperm cells

• produces inhibin (too much sperm)

Leydig Cells

• also known as interstitial cells

• in the connective tissue between seminiferous tubules

• secretes testosterone

Ejaculation Pathway of Sperm

• testes → epididymis → vas deferens → seminal vesicle → ejaculatory duct → urethra

Seminal Fluid (Semen)

• sperm cells + fluids

Gonadotropin-Releasing Hormone (GnRH)

• peptide hormone

• made and released by neurons in the hypothalamus

• causes anterior pituitary to make and release FSH & LH

Follicle-Stimulating Hormone (FSH)

• peptide hormone

Males

• stimulates sertoli cells to provide nourishment during spermatogenesis

Females

• stimulates follicles to develop eggs

• puberty changes - breast development, menstruation

• inhibited by estrogen (and progesterone)

Luteinizing Hormone (LH)

• peptide hormone

Males

• stimulates leydig cells to produce testosterone

Females

• surge of LH → ovulation → forms corpus luteum

Testosterone

• steroid hormone

• promotes development of male secondary sexual features & sex drive

• helps with spermatogenesis

Steroids

• synthetic derivatives of testosterone

• promotes muscle growth

• prescribed to males with low testosterone or HIV patients

• abused by some athletes and bodybuilders

Estrogen

• steroid hormone

• thickens endometrium

• inhibits FSH

• stimulates hypothalamus to release GnRH → increases LH (surge) → ovulation

Progesterone

• steroid hormone

• produced by corpus luteum

• thickens endometrium

• inhibits LH & FSH (can lower GnRH)

Menstrual Cycle

• ensures that the ovum is released at the same time that the uterus is most receptive to a fertilized egg

• typically 28 days

• consists of 2 interconnected cycles - ovarian & uterine cycle

• controlled by ovarian & pituitary hormones

Ovarian Cycle

• occurs in the ovaries

• follicular phase, ovulation, luteal phase

Uterine Cycle

• begins on the first day of menstruation (lasts ~5 days)

• estrogen & progesterone → endometrium thickens from day 6-23

• no fertilization → corpus luteum disintegrate → estrogen & progesterone decrease → menstruation

Excretory System

• filters blood & removes waste

Filtrate

• ions, water, glucose, & any other particles that can enter the Bowman’s capsule; urine

Ureters

• tubules that carry urine to the bladder

Bladder

• collects and holds urine

Urinary Sphincter

• controls flow of urine

Urethra

• tubule connected to bladder to excrete urine from the body

Kidneys

• removes waste

• maintains blood pH & water balance

Renal Cortex

• outer layer of kidney, filtering layer

Renal Medulla

• middle/inner layer of kidneys

Renal Pelvis

• centre of kidneys, vessels continuous to ureters

Renal Artery

• carries blood to the kidneys

Renal Vein

• carries blood away from the kidneys

Renal Pyramids

• cone-shaped tissues that contain nephrons

Nephrons

• functional unit of kidneys

• long tubules with series of blood vessels

• filtration & reabsorption

Deamination

• removal of an amino group to form ammonia (toxic) & a keto acid

• aquatic - ammonia excreted by gills, may convert to urea by liver

• mammals - breakdown protein/a.a to ammonia, then urea

• birds - breakdown of purines to uric acid

Keto Acid

• can be used for for energy in the liver or converted into glucose/fat (for respiration)

Glomerulus

• a cluster of capillaries enclosed in the Bowman’s capsule for filtration

• permeable to small solutes but not large ones (blood cells, proteins)

Non-selective filtration

• any solute small enough will be filtered; no selection

Proximal Convoluted Tubule

• active transport of Na+, K+, & glucose

• anions follow via electrostatic attraction, water by osmosis

• H+ actively transported into filtrate, NH3 produced by nephrons follow passively

Descending Loop of Henle

• cells are permeable to water, but only slightly to ions → maintain concentration gradient

• higher [Na+] in medulla than filtrate → Na+ diffuses out of filtrate

• [Na+] of filtrate is highest at the bottom of the loop (most water has left)

Ascending Loop of Henle

• Thin segment

  • impermeable to water, slightly permeable to solutes

  • Na+ diffuses out

• Thick segment

  • as Na+ leaves, concentration gradient weakens → Na+ actively transported out of filtrate

Distal Convoluted Tubule

• reabsorption depends on body’s needs - similar to proximal

• H+, K+, and medications secreted into filtrate - H+ due to acidic blood pH

Acid-Base Buffer

• acidic

  • H+ leaves blood and into filtrate

  • HCO3- is reabsorbed by blood

• basic

  • H+ does not leave, HCO3- not reabsorbed

Collecting Duct

• water reabsorbed by osmosis

• some urea may diffuse out due to high [urea], but most stays in filtrate

• Na+ actively transported out, anions follow (depends)

• urine is formed

Nervous System

• regulates homeostasis & controls actions of the body

• electrochemical signals, allows for quick changes

• 2 parts - CNS & PNS

Central Nervous System (CNS)

• nerves of the brain & spinal cord

• receives and processes information

Peripheral Nervous System (PNS)

• all nerves other than CNS, relays information between organs/muscles & the CNS

• 2 parts - somatic & autonomic

Somatic Nervous System

• controls voluntary motion; skeletal muscles, bones, skin

Sensory Somatic Nerves

• carries sensory information from the body to the CNS

Motor Somatic Nerves

• carries voluntary movement commands from the CNS to the body

Autonomic Nervous System

• controls involuntary motion; contains special motor nerves that control internal organs

• 2 nerves - sympathetic nerves & parasympathetic nerves

Sympathetic Nerves

• prepares the body for action (fight-or-flight)

Parasympathetic Nerves

• returns the body to normal resting levels after adjustment to stress (rest & digest)

Glial Cells

• important for structure support & metabolism of nerve cells

• non-conducting cells (does not relay signals)

Neurons

• specialized nerve cells that conduct nerve impulses

Sensory Neurons (Afferent Neurons)

• relays impulse from sensory receptor to interneuron

• found in ganglia

Sensory Receptors

• receives stimuli and forms nerve impulses

Ganglia

• a cluster of nerve cell bodies in the PNS

Interneurons (Association Neurons)

• receives and processes information to decide where it gets fired (for a proper response)

• links sensory & motor neurons

• in the CNS

Motor Neurons (Efferent Neurons)

• receives impulse from interneurons & triggers effectors (e.g. muscles, glands, etc.) to respond

Dendrites

• receives signal from a receptor (sensory) or another neuron

• conducts the impulse towards the cell body

Cell Body

• houses the nucleus & other organelles

• processes signals from dendrites

Axon

• transmits signals for other neurons to pick up

• larger axon diameter → faster transmission speed

• conducts the impulse away from the cell body

Axon Terminal

• allows signal to be picked up by other neurons

• converts electrical signal back to chemical

Myelin Sheath

• white coat of lipids & proteins, has many layers

• insulation → prevents loss of charged ions → maintain voltage & signal strength

Schwann Cells

• specialized glial cells that forms the myelin sheath

Nodes of Ranvier

• gaps between the myelin sheath that allows impulses to jump → speeds up transmission

Neurilemma

• PNS nerves only

• a thin membrane around the myelin sheath that promotes regeneration of the axon

White Matter

• neurons with myelin sheaths

Grey Matter

• neurons without myelin sheaths

• damage is usually permanent

Multiple Sclerosis

• autoimmune disease, immune system damages myelin sheath

• damaged myelin forms hard/scar-like tissue → no insulation → disrupt nerve impulse transmission

• symptoms - double vision, speech difficulty, partial paralysis, jerky limb movements

Reflexes

• sudden, involuntary responses to certain stimuli