Homeostasis

Homeostasis

Process by which a constant internal environment is maintained despite continuous changes to the external environment

How do most homeostatic mechanisms work?

On a negative feedback loop - System only needs to work if the “pre-set” condition is not being kept.

“Pre-Set” Condition

“Normal” condition your body tries to maintain. Everyone is different - some people have higher heart rates, body temperatures, metabolism, etc.

Three functional components of a homeostatic mechanism

Monitor, coordinating centre, regulator

Monitor

A receptor that notes any change, reports preset limit to control centre.

Coordinating Centre

Interprets the monitor to put regulators into actions —> tends to be the creator of the “pre-set” limit

Regulator

Utilizes organs, hormones & chemicals to effect various parts to return to the preset conditions

Thermoregulation

Regulation of body temeperature - body’s thermostat.

Thermoregulatory center

Located in the preoptic area of the hypothalamus. Sets the body’s set point and regulates temperature homeostasis. Temperature sensors receive information via nerve cells called thermoreceptors.

Vasoconstriction

Happens when conserving heat. Blood vessels narrow (arterioles constrict), reducing blood flow to the skin —> heat loss from the skin decreases since less blood flows to the skin’s surface, flows closer to the core.

Vasodilation

Occurs when too hot. Blood vessels widen (arterioles dilate), allowing more blood to flow near the skin surface. Heat loss from the skin increases as the blood loses heat to the environment.

Kidneys

Born with 2 - hold 25% of your blood at any given time.

Parts of the urinary system

Kidneys, Ureters, Bladder, Sphincters, Urethra

Homeostatic uses of Kidneys

Regulates water volume, concentration, & pH levels. Influences red blood cell production and blood pressure. Filters blood to create urine.

Parts of kidneys

Renal pelvis, Ureter, Medulla, Cortex

Kidneys filtering blood

The body takes nutrients from food —> converts them to energy. After body has taken the food components it needs, waste products are left behind. Kidneys filter your blood at a rate of a bathtub-full per day (200L). Remove the “bad stuff” and allow you to keep “good stuff”

How much do kidneys filter per minute?

Kidneys remove 120 m: of “bad stuff”, gives back 119 mL of the "water content. 1 mL —> urine. Goes to the bladder via the ureter.

Bladder

Urine stored in bladder, stretchable like a stomach (ruggae). Stretch receptors signal when the bladder is getting full. Urinary sphincter at the base of the bladder controls release into urethra. When sphincter relaxes → pee.

mL in bladder.

Internal sphincter involuntary, external voluntary, but…

At 200 mL - urge
At 400 mL - panic
At 600 mL - release without permission

Nephrons

Similar to the villi - the functional group of the kidney. Key worker in filtering your blood & returning much of the needed water, ions, amino acids and glucose back into the system while removing creatine and urea.

Nephrons 2 main parts.

A ball formed by small blood capillaries (glomerulus) - and a small tubule (renal tubule)

Good and bad things in the filtration of blood

Good, want back: Water, ions, amino acids & glucose
Bad, want to go: Creatine, urea, excess ions, amino acids, and glucose

Parts of the nephron

Afferent arteriole, efferent arteriole, glomerulus, Bowman’s capsule, PCT, Descending loop, Loop of Henle, Ascending loop, DCT, Collecting duct

Three steps of filtering blood

Glomerular filtration, tubular reabsorption, tubular secretion

Glomerular Filtration

First key interaction: Between glomerulus & Bowman’s capsule - blood under tremendous pressure, squeezed through glomerulus to lumen of Bowman’s capsule. Bigger molecules like blood cells and proteins blocked, stay in blood. Salt, water, amino acids, sugar, hydrogen ions, HCOB, pushed through. Water is the largest component of the new filtrate (120 mL/600 mL)

Glomerulus

Arterioles wrapped together, squeezed tight

Where is filtrate sent

Sent along 3 cm long ubule. Proximal convoluted tubule —> nephron loop —> distal convoluted tube —> collecting duct (1 mL of filtrate, 119 mL reabsorbed by body)

Tubular Reabsorption

Long curly shape allows for more time & space to reabsorb useable stuff.

PCT reabsorption

Tries to retrieve most of the good stuff. Integral proteins use active transport to pull sodium from filtrate, Cl- follows. Creates osmotic gradient - water pulled out into interstitial space and then diffuses into capillary. Reabsorbs 80% of water.

Interstitial space

Between capillary & nephrons

Henle Reabsorption

Descending loop sees whether outer medulla has higher or lower concentration of salt. If lower, NaCl passively diffuses. Loop of Henle narrows, creates pressure that shoots it into ascending loop. Keeps checking and passively diffusing. Ascending loop checks again - if there’s still too much salt, actively moves filtrate (how kidney stones are formed).

Distal Convoluted Tube Reabsorption

Regulatory hormones & chemicals also focus on this spot. 10-15% extra water out of filtrate if needed, through active transport. Couple of methods to trick your body into taking out more water - various hormones and chemical messengers.

Collecting Duct Reabsorption

Draws out some urea to help with osmotic pressure of previous steps.

Tubular Secretion

Actively transports out some selective waste

Juxtaglomerular Apparatus

Every time blood is pushed in - checks the pressure. Doesn’t know why it is so low. BP goes own because of dehydration, cut, internal injury. Specialized juxtaglomerular cells feel the push into the Bowman’s capsule like a blood pressure cuff would.

Blood pressure low

Juxtaglomerular apparatus releases renin into blood - finds chemical angiontensinogen → angiotensin.

Angiotensin

Two purposes -

More volume: talks to aldosterone, found in adrenal gland, goes immediately to nephron. Every integral protein that can actively move water across, do so now. Moves out positive ions - water follows, increase in water = increase in pressure.

Constrict blood vessels.

Headaches

Osmoreceptors at hypothalamus judge the amount of water in blood. Too low —> hurts. Not just water needed —> metal ions needed to make water move in the nephron. Stop sweating. Brain signal to Juxtaglomerular Apparatus to send out ADH, which makes is way to the DCT.

Dehydration response

Brain signal to juxtaglomerular apparatus. Send out ADH (Antidiuretic Hormone), which makes its way to DCT. Tells it to absorb any positive ion - any water made to leave. When ADH kicks in - thirst response.

Blood Sugar Regulator

Pancreas - Just below liver. At islands of Langherhan (Different areas = different hormones)

Blood sugar Hypothalamus

Sets limit for blood sugar within your blood

Limit for blood sugar

(70 to 80 mg/dL 8 hours after eating and about 120 mg/dL 2 hours after eating)

What hormones control blood sugar?

Insulin, Glucagon

Insulin

Released by beta cells if BS is too high. Extra BS → glycogen (muscle & liver cells)

Glucagon

Released by alpha cells if BS is too low - targets liver. Glycogen broken down into glucose, released into bloodstream.

Hormones secreted by pancreas

Insulin, Glucagon, Gastrin, Somatostatin, Vasoactive Intestinal Peptide

Gastrin

Aids digestion by stimulating certain cells in the stomach to produce acid

Somatostatin

When other pancreatic hormones, such as insulin and glucagon get to high, somatostatin is secreted to maintain a balance of glucose and/or salt in the blood.

Vasoactive Intestinal Peptide

Helps control water secretion and absorption from the intestines by stimulating the internal cells to release water and salt into the intestines.

Thyroid Gland

Butterfly shaped gland found before larynx, monitor for releasing thyroxine (T4), produces calcitonin.

Control Centre for thyroid gland

Hypothalamus & Pituitary

Thyroxine production phases of life

Production takes off during puberty - responsible for growth & metabolism. Takes off during pregnancy, but after birth, doesn’t know what to do next, and gets thyroid problem.

Thyroid production of calcitonin

Tells your body to have lots of calcium and stick it on your bones during puberty

Thyroid process

Hypothalamus releases TRH, goes to Anterior Pituitary Gland, releases TSH, heads to thyroid, which releases either thyroxine or calcitonin.

Negative feedback loop thyroxine

Release of T4 inhibits TRH release from hypothalamus

Hypothyroidism

Too little T4 - caused by low iodine.
Symptoms: Cold intolerance, weight gain, dry skin, moody, tired, goiter.

Hyperthyroidism

Too much T4 - caused by autoimmune disorder, too much iodine, iodine full meds
Symptoms: Weight loss, always hungry, excessive sweating, protruding eyes, sensitive to heat

Parathyroid gland

Four smaller glands embedded in the thyroid gland, controls calcium levels.

High blood calcium levels

Hypothalamus detects, thyroid stimulated, calcitonin released, bones take in more Ca2+

Low blood Ca2+ levels

Hypothalamus detects, parathyroid detects, PTH released, Bones give back Ca2+, intestines hunt for Ca2+, kidneys absorb Ca2+

Pituitary Gland

Master gland, one centimeter in diameter, found at bottom of the hypothalamus, two lobes (anterior, posterior). So deep into your brain you have to accept what it’s going to do to you.

Posterior Lobe Pituitary Gland

Stores and releases hormones that are typically produced in the hypothalamus: ADH, Oxytocin

ADH/Antidiuretic hormone

Helps body conserve water, prevent dehydration

Oxytocin

One of the few “positive feedback” hormones. Happy drug. Men need physical contact for it to release. Women get it automatically every 28 days - reaches highest peak when about to give birth. Causes uterine contractions → period pains.

Anterior Lobe (Pituitary Gland)

Produces, stores and releases its own hormones: Human Growth Hormone, Thyroid Stimulating Hormone, ACTH (Adrenocorticotropic Hormone), FSH (Follicle stimulating hormone), LH (Luteinizing Hormone), Prolactin (Lactating Hormone)

Human Growth Hormone

To blame for growing pains - when too much released at once. Increases metabolic rate, protein synthesis, cell division, growth plate metabolism, breaking down of brown adipose tissue. Growth plates extend and fuse.

HGH Injections

Make you feel younger, help you build muscle, but cause pains

Thyroid Stimulating Hormone

Works with HGH, really goes of when HGH goes off - Both present in pregnancy

ACTH

Adrenocorticotropic hormone - Talks to adrenal gland - under stress hormone

FSH

Follicle stimulating hormone - makes sperm & egg

LH

Luteinizing Hormone - Makes gametes function

Prolactin

Lactating Hormone - To make milk

Adrenal Gland

Located at the top of the kidneys. Two layers.
Outer Layer: Cortex
Inner layer: Medulla
Produces two main groups of corticosteroid hormones:
Glucocorticoids: Hypothalamus & Pituitary Gland
Mineralcorticoids: Kidney

Adrenal Gland Layers, Type of hormones

Cortex: Necessary for day-to-day life
Medulla: Emergency responses

Inner Medulla - adrenal glands

Short term stress, need it to perform well. Performance Curve. HYpothalamus has a direct neural line - release of epinephrine and norepinephrine

Epinephrine

Fight, flight or freeze response. Heart rate increases, breathing rate increases. Blood pressure flow to extremities decreased. Liver function increases (glycogen to glycose, spikes blood sugar). Pupils dilate - other senses dulled.

Norepinephrine

Works with epinephrine in responding to stress - can also cause vasoconstriction, which results in high blood pressure

Outer cortex - Adrenal Gland

Dont want. Hypothalamus produces CRH, stimulates the pituitary gland to release ACTH - causes Adrenal gland to relase Cortisol & aldosterone

Cortisol

Increase blood sugar, decreases inflammation, decreases immune response, inhibits connective tissue growth

Aldosterone

Increases Na+ absorption at DCT (Crave more salt). Increases blood pressure. Feel bloated - retain more water.

If outer cortex active for too long…

Serious concerns - Get used to long term stress, but…

New thresholds established for:
Blood sugar levels → Adult onset diabetes

Blood pressure → too high = stroke

Heart rate → Too much = heart attack

Types of neurons

1. Sensory Neurons

2. Interneurons

3. Motor Neurons

4. Neurons of the Brain

Types of sensory neurons

1. Photoreceptors

2. Chemoreceptors

3. Thermoreceptors

4. Mechanoreceptors

5. Nocioreceptors

Male Reproductive System

Hypothalamus releases GnRH (Gonadotropin Releasing Hormone) to talk to Anterior Pituitary Gland, which releases FSH or LH.

Male FSH

Enters testes, stimulates sertoli cells to make sperm but the sperm is not functional

LH Male

At puberty - talks to interstitial cells of Leydig (in testes) to start making testosterone. Talks to FSH → change the way you make sperm to make it functional. Also causes secondary sex characteristics: Deep voice, facial hair, sex drive.

Negative Feedback Loop Male Reproductive System

When too much sperm - Hypothalamus turns off production. Rising levels of testosterone act on hypothalamus & anterior pituitary to inhibit GnRH, FSH & LH.
Sertoli cells produce inhibin hormone, released into blood when sperm count is too high - inhibits GnRH & FSH, causes spermatogenesis to slow down

Sperm Life Expectancy

Sperm has a life expectancy - breaks down and makes anew

Male Infertility

Look to the man first if a couple is having trouble getting pregnant - not enough sperm, sperm isnt functional

Female Reproductive System

Hypothalamus controls GnRH stimulates Anterior Pituitary to releasee FSH and LH

FSH Women

Stimulates development of egg cells, called ova, which develop in structures called follicles - Follicle cells produce inhibin, inhibits FSH production. Talks to eggs (there since birth) in growing follicles - tells 4 to mature, but only one makes it. When it finds an egg, estrogen elevates to shut off any more FSH, talks ack to pituitary and tells LH to go.

LH Women

Tells body when egg is ready for release. Tells body when egg is ready for release, sends out ping - actual sensation that egg has been released.

Ping/Egg Release

Temperature slightly elevated for 3-4 hours when egg is released - for the next 48 to 72 hours, primed to get pregnant.

Egg Release Husk

Curls back in, the brain of any future baby (Corpus Luteum) - created by progesterone.

Progesterone

Tells the body when it is ready to get pregnant - turns off anterior pituitary, tells hypothalamus to shut off system. When people aren’t pregnant - leaves very quickly after egg release. Makes birth control pill - tells your body that you’re pregnant and to stop releasing eggs.

Age - Ovaries

Figure out age through Corpeus Luteum - stays as a scar on your ovaries to know the number of ovulations

How many times is your body prepared to get you pregnant?

Once a year

Endometrium

Fluffy pillow that egg lands on in uterus - becomes placenta when pregnant, leaves when on your period. Need fat to form, when you don’t have enough fat gain - no period.

Pregnancy

Egg is fertilized. GnRH tells pituitary gland to release more LH and less FSH, placenta produces more estrogen and progesterone. Relaxin released. Intestines absorb more H2O and nutrients. Prolactin released. oxytocin released and keeps increasing, almost exponentially.

Relaxin Pregnancy

Allows skin to stretch & relaxes ligaments for labor