Chapter 15- Homeostasis

Question 1

Define homeostasis

Answer 1

The maintenance of a dynamic equilibrium stimulated by the monitoring of small changes in the body’s metabolic state

Question 2

Give an example of a positive feedback system

Answer 2

Oxytocin stimulates the uterus to contract, pushing the baby’s head harder against the cervix and triggering more oxytocin to be released

Question 3

Describe the difference between an endotherm and an exotherm

Answer 3

An endotherm is capable of regulating their own body temperature
An ectotherm has to use their external environment to regulate their body temperature

Question 4

How is the Namaqua chameleon physiologically adapted to its role as an ectotherm?

Answer 4

Increased heart rate in the morning
Changes colour through the day to absorb more heat

Question 5

Which part of the brain organises responses to change in temperature?

Answer 5

The hypothalamus

Question 6

Describe the ways that endotherms cool down

Answer 6

Vasodilation- arterioles near the surface of the skin expand and radiation increases, cooling the animal down
Sweating- As sweat evaporates from the surface of the skin heat is lost
Reducing insulation of hair/ feathers- erector pilli muscles in hair relax allowing hair to lay flat to the skin

Question 8

Apart from the opposite of the cooling effects, what might an ectotherm do to warm up?

Answer 8

Shivering- rapid involuntary muscle contraction of large muscles in the body generates heat

Question 9

Describe the controlling of thermoregulation

Answer 9

Two areas in the hypothalamus- the heat loss and the heat gain centres. Sends impulses through the autonomic nervous system to effectors in skin that trigger the appropriate response

Question 10

Which vein in the liver transports oxygenated blood from the intestines?

Answer 10

The hepatic portal vein

Question 11

What are the other two major blood vessels supporting the liver?

Answer 11

Hepatic Vein and the Hepatic Artery

Question 12

Name the three main metabolic waste products in animals

Answer 12

-Carbon dioxide
-Bile Pigments
-Nitrogenous waste products (urea)

Question 13

Describe the ultrastructure of the liver

Answer 13

Liver cells are called hepatocytes that have large nuclei, prominent golgi apparatus and large amounts of mitochondria. These hepatocytes are surrounded by spaces called sinusoids where blood from the hepatic artery and portal vein mix. Sinusoids also contain Kuppfer cells which act as macrophages. Hepatocytes secrete bile into spaces called canaliculi, from which bile drains into the bile ductules and are taken to the gall bladder

Question 14

What is the name of the biological cycle involved in deamination?

Answer 14

Ornithine cycle

Question 15

Describe the stages of the ornithine cycle

Answer 15

Deamination produces ammonia
Ammonia enters the cycle and combines with ornithine to produce citruline. Citruline is dehydrated to produce arginine, which is hydrolysed to produce urea and ornithine, regenerating the cycle

Question 16

Describe two minor roles of the liver

Answer 16

Carbohydrate metabolism- involved in insulin and glucagon action
Detoxification (eg catalase action)

Question 17

Describe liver cirrhosis

Answer 17

A disease where normal liver tissue is replaced by scar tissue- normally caused by excessive alchohol consumption

Question 18

What are the two homeostatic roles of the kidney?

Answer 18

Excretion and osmoregulation

Question 19

What are the names of the blood vessels supporting the kidneys?

Answer 19

Renal artery and renal vein

Question 20

Describe the structure of the kidneys

Answer 20

Three regions- cortex (outer layer) where blood filtering takes place. Has millions of tiny structures called nephrons that act as filtering units.
Medulla (inner layer) contains the renal pyramids and the collecting ducts
Pelvis (basin) where urine is collected before being passed to the bladder

Question 21

Describe the structure of the kidneys in order

Answer 21

The bowman’s capusle- Cup shaped structure containing the glomerulus
Proximal convoluted tubule
Loop of Henle
Distal convoluted tubule
Collecting duct

Question 22

Which regions of the nephron are susceptible to ADH?

Answer 22

Distal convoluted tubule and the collecting duct

Question 23

What will have changed in the blood concentration after filtration through the kidneys?

Answer 23

Urea would be greatly reduced but levels of glucose and other substances would be relatively the same depending on how much of an excess there was in the first place

Question 24

How does blood in the glomerulus create high pressure?

Answer 24

The afferent arteriole is much wider than the efferent arteriole, creating a pressure that forces blood out of the capillary wall, across the basement membrane and finally across the podocytes all which act as an additional filter.

Question 25

What is the name of the liquid that enters the capsule?

Answer 25

Filtrate- containing glucose, salt, urea and other substances in the same concentration as they are in blood plasma

Question 26

Describe the structure and function of podocyte cells

Answer 26

Extensions called pedicels wrap around capillaries and block any large platelets or proteins that might have squeezed through from entering the blood

Question 27

What is the purpose of the rest of the nephron if all of the filtrate is filtered in the bowman’s capsule?

Answer 27

Reabsorption - a lot of essential molecules are filtered out and need to be fine tuned so the concentration staying in the blood is right

Question 28

What is reabsorbed in the proximal convoluted tubule?

Answer 28

All glucose, amino acids, vitamins and hormones Also 85% of water (passively transported) and sodium ions (actively transported)

Question 29

What occurs at the end of the proximal convoluted tubule?

Answer 29

The filtrate is isotonic with the arterioles surrounding it

Question 30

Which section of the nephron allows mammals to produce urine more concentrated than their own blood?

Answer 30

The loop of Henle- acts as a countercurrent multiplier

Question 31

How does the loop of Henle create an increasing solute concentration?

Answer 31

The ascending limb is impermeable to water and actively pumps out sodium and chloride ions, creating a high concentration in the medulla tissue. The descending limb is partially permeable to water but not to sodium and chloride ions, and due to the activity of the ascending limb water passes into the tissue fluid, leaving behind very concentrated filtrate.

Question 32

Why is it important to control the water potential of tissues?

Answer 32

Because if water moves in or out of cells in large volumes it could cause death

Question 33

Where is ADH produced?

Answer 33

The hypothalamus, and secreted into the posterior pituitary gland

Question 34

What is the effect of ADH?

Answer 34

Increases permeability of the distal convoluted tubule and the collecting duct to water

Question 35

Is ADH a steroid or non steroid hormone?

Answer 35

Non-steroid - It triggers a cascade of events internally in the cell by binding to external receptors

Question 36

What is the name of the secondary messenger triggered by ADH inside the cells of the nephron?

Answer 36

cAMP- levels of cAMP that are high enough causes a cascade of events - Vesicles containing aquaporins in the cells fuse to the cell surface membrane More ADH- more water channels inserted into the walls. Less ADH- the opposite effect

Question 37

How does the hypothalamus detect changes in water?

Answer 37

Osmoreceptors detect changes in ion concentrations in the blood and stimulate the release of ADH

Question 38

Describe how pregnancy tests use urine as an indicator for pregnancy

Answer 38

Monoclonal antibodies are produced using mice injected with HCG. The B cells produced are harvested and fused with a myeloma (cancer) that makes them divide rapidly. The test containing mobile antibodies have small coloured beads attached to them- if a woman has hCG present these will bind. They move up the test and stick to immobilised antibodies, forming a pattern that is used diagnostically

Question 39

Give three examples of urine diagnosis

Answer 39

The use of anabolic steroids Drug Testing Diabetes 1 & 2

Question 40

Give two causes of kidney failure

Answer 40

Protein in urine- basement membrane or podocytes are damaged, allowing plasma proteins through Blood in urine

Question 41

Describe the differences between haemodialysis and peritronal dialysis

Answer 41

Haemodialysis- uses a dialysis machine using an artificial basement membrane Peritoneal dialysis- makes use of natural dialysis membranes in the abdomen (peritoneum)