SBI4U Unit 4 Homeostasis

Homeostasis

The maintenance of a steady internal environment

Dynamic Equilibrium

Internal conditions fluctuating within small ranges

Feedback Systems

Mechanisms in the body used to monitor and adjust internal conditions. Contains a Sensor, Control Center, and Effector

Sensor

Part of a Feedback System that detects changes in an environment, sends information to the control center.

Control Centre

Part of a Feedback System that processes inputs from sensors, decides on an appropriate response and sends signals to effectors

Effector

Part of a Feedback System that carries out responses decided by the control centre to restore homeostasis

Negative Feedback Loop

Feedback Loop where the body works to reverse a change, bringing a variable back to within normal range

Positive Feedback Loop

Feedback Loop where outputs from a system strengthen a change in a variable to accomplish a goal quicker.

Thermoregulation as a Feedback Loop

Sensor: Muscles producing heat after exercise

Effectors:

• If too hot, blood vessels in skin dilate, sweat glands release water to cool body

• If too cold, skeletal muscles contract, blood vessels in skin constrict

Excretory System

Organ System that removes waste from blood

List: Major Organs in the Excretory System

1. Kidneys

2. Ureters

3. Bladder

4. Urethra

Kidneys

Organ that removes waste & water from blood, produces urine

Ureters

Organ that transports urine

Bladder

Organ that stores urine

Urethra

Organ that passes urine to outside of body

List: Four Functions of the Excretory System

1. Remove waste from blood

2. Maintain water balance

3. Keep ions in blood in balance

4. Secrete hormones

Renal Arteries

Blood vessel that carries blood to kidneys

Renal Cortex

Outer region of the kidney

Renal Medulla

Inner cone-shaped regions of the kidney

Renal Pelvis

Central Space/Cavity of the kidney

Nephron

Functional unit of the kidney within renal medulla and renal cortex: filters substances from blood to turn it into urine

Bowman’s Capsule

Structure for Filtration in the nephron, surrounds glomerulus

Glomerelus

Network of capillaries in Bowman’s Capsule, performs filtration: Impermeable to large molecules and RBC’s, permeable to water, ions, small molecules and urea

Filtrate

Fluid pushed from glomerulus into Bowman’s Capsule, contains water, ions, small molecules and urea

Proximal Tube

First segment of the nephron tubule after Bowman’s Capsule where substances are mostly reabsorbed back into blood

Distal Tube

Segment of the nephron tubule after the Loop of Henle where substances are mostly secreted back into the tubule

Loop of Henle

Loop that descends into medulla, draws water out of filtrate through osmosis to concentrate urine. At the bend, permeability changes to become impermeable to water and slightly permeable to solutes, and solutes are drawed out to maintain salty environment in medulla

List: Four steps of Urine Formation

1. Glomerular Filtration

2. Tubular Reabsorption

3. Tubular Secretion

4. Re-absorption

Glomerular Filtration (Step)

First step in urine formation: Water and small solutes are pushed into Bowman’s Capsule from blood vessels

Tubular Reabsorption (Step)

Second step in urine formation: 65% of filtrate is reabsorbed back into the blood. Occurring mostly in the proximal tubule

Tubular Secretion (Step)

Third step in urine formation: Molecules move into tubule, H+ ions are actively secreted to maintain pH. Occurring mostly in the distal tube

Reabsorption (Step)

Fourth step in urine formation: Water is absorbed back into blood via osmosis to concentrate urine. Occurring in collecting duct

Collecting Duct

Final segment of the nephron tubule that reabsorbs water back into blood to concentrate urine

ADH (antidiuretic hormone)

Hormone produced by posterior pituitary, regulates osmotic pressure by causing kidneys to increase water reabsorption by changing permeability of distal tube and collecting duct.

List: Sensor & Response to ADH if dehydrated

Sensor: Blood plasma is very concentrated due to less water

Response: Receptors in hypothalamus send a signal to posterior pituitary to release ADH

List: Sensor & Response to ADH if overhydrated

Sensor: Blood Plasma is too dilute

Response: Receptors in hypothalamus send a signal to posterior pituitary to stop ADH release

Pituitary Gland

Gland at the base of the brain that releases hormones in response to signals from hypothalamus (ADH), has a posterior lobe and anterior lobe

Diuretics

Substances that increase urine production by inhibiting release of ADH, leading to increase urine volume

Renin

Enzyme released by kidneys when blood pressure is low, triggers the release of aldosterone

Aldosterone

Hormone secreted by adrenal cortex that stimulates absorption of Na+ back into the blood

Adrenal Glands

Glands on top of each kidney that produce different hormones

List: Sensor & Response to low blood pressure

Sensor: Blood pressure is low

Response: Kidneys release renin, then aldosterone is secreted by adrenal cortex, stimulating the absorption of Na+ back into blood, allowing H2O to be absorbed, increasing volume and therefore increasing blood pressure

Endocrine System

Organ system that releases hormones into bloodstream

Hormones

Chemical messengers that trigger a biochemical reaction

List: Important Endocrine Glands

• Pituitary Gland

• Hypothalamus

• Thyroid Gland

• Adrenal Gland

• Pancreas

• Testicles/Ovaries

Posterior Lobe of Pituitary Gland

Lobe that release ADH and Oxytocin

Anterior Lobe of Pituitary Gland

Lobe that releases ACTH, FSH, LH

List: Two Types of Hormones

1. Steroid Hormones

2. Water-Soluble Hormones

Steroid Hormones

Type of Hormone made from cholesterol, enters target cell easily through cell membrane to bind to receptor proteins and regulate specific genes in the cell

Water-Soluble Hormones

Type of Hormone that binds to specific cell surface receptors as they can’t pass through cell membrane. They promote cAMP, activating an enzyme cascade

Enzyme Cascade

Series of enzyme activations triggered by one another

cAMP (cyclic adenosine monophosphate)

Molecule produced from ATP that activates an enzyme cascade

Adrenal Medulla

Inner region of the adrenal gland, releases epinephrine and norepinephrine, regulates the fight or flight response. Short term stress

Fight or Flight Response

Rapid stress response, nervous system triggers the release of epinephrin and norepinephrine.

List: Effects of Epinephrine and Norepinephrine

• Higher Metabolism

• Higher Breathing Rate & Heart Rate

• Higher Blood Pressure

• Glycogen —> Glucose in Liver

• Pupils Dilate

• Pain Tolerance Decreases

• Insulin is Inhibited

• Nervous System activates aldosterone and ADH

Prostaglandins

Hormones that produce an effect to adjust to changes from stress

Cortisol

Hormone produced by adrenal cortex when ACTH is present, released in response to long term stress, promotes metabolism and increases breathing rate and heart rate. Higher levels of cortisol suppresses ACTH.

Epinephrine/Norepinephrine

Hormones released by the adrenal medulla in response to short term stress. Key in fight-or-flight response

Adrenal Cortex

Outer region of adrenal gland, produces cortisol and aldosterone

ACTH (adrenocorticotropic hormone)

Hormone released by anterior pituitary gland, targets adrenal cortex to produce cortisol

GnRH

Hormone released by hypothalamus, targets anterior pituitary and causes it to release FSH and LH

Hypothalamus

Part of brain that contains pituitary gland, also releases GnRH

FSH (Follicle-Stimulating Hormone)

Hormone released by anterior pituitary, causes secretion of inhibin
Males: Sperm Production
Females: Estrogen Production, Growth of Follicles

LH (Luteinizing Hormone)

Hormone release by anterior pituitary
Males: Testosterone Production
Females: Progesterone Production, Triggers Ovulation

Testosterone

Male Reproductive Hormone produced by testes, activates secondary sex characteristics. High levels inhibit release of LH and GnRH

Inhibin

Hormone produced by testes (males) and ovaries (females), inhibits FSH release and regulates gamete production through feedback loops

Testes

Male reproductive organ, produces sperm and testosterone

Estrogen

Female Reproductive Hormone produced by ovaries, activates secondary sex characteristics. High levels of estrogen inhibits FSH and also causes LH secretion

Ovaries

Female reproductive organ, produces eggs, estrogen and progesterone

Progesterone

Female Reproductive Hormone produced by ovaries, prepares uterus for an embryo by inhibiting ovulation and preventing contractions

Follicles

Structures in the ovaries that contain ocytes, secretes estrogen

Oocytes

Immature female egg in follicle, bursts out of ovary when it matures to become a mature egg

Corpus Luteum

Structure formed from a ruptured follicle, secretes pregnancy hormones to inhibit FSH and LH production. Degenerates when no pregnancy occurs

Menstruation

28 day cycle of hormones where the uterus lining sheds, occurs when egg is not fertilized

List: Four Phases of Menstrual Cycle and lengths

1. Flow Phase (5 days)

2. Follicular Phase (8 days)

3. Ovulatory Phase (1 day)

4. Luteal Phase (14 days)

Flow Phase

First phase of menstrual cycle: Shedding of uterus lining

Follicular Phase

Second phase of menstrual cycle: FSH stimulates follicles to develop in ovary, secreting estrogen

Ovulatory Phase

Third phase of menstrual cycle: Egg bursts out of follicle, ruptured follicle differentiates into corpus luteum

Luteal Phase

Fourth phase of menstrual cycle: Corpus Luteum secretes estrogen, progesterone and inhibin, then deteriorates to begin menstruation again