Homeostasis + Osmoregulation

Question 1

What is the definition of homeostasis?

Answer 1

Homeostasis is the physiological systems maintaining internal conditions within restricted limits to ensure optimum conditions for enzyme function and cell control.

Question 2

What are the main factors controlled by homeostasis?

Answer 2

The main factors controlled by homeostasis include metabolic waste (e.g., CO2 and urea), core body temperature + blood pH (providing optimum and preventing denaturation), blood glucose concentration (affects water potential and respiratory substrate availability for cells), water potential of blood, and concentration of respiratory gases in blood.

Question 3

How does the endocrine system help maintain homeostasis?

Answer 3

The endocrine system is made up of glands (have good blood supply) which produce hormones carried in the blood to bind to complementary receptors on target organs, bringing about slower, long-term changes to maintain homeostasis.

Question 4

What is the role of the pituitary gland in the endocrine system?

Answer 4

The pituitary gland is known as the ‘master gland’ and coordinates the release of hormones from other glands.

Question 5

What hormones are produced by the thyroid and what are their functions?

Answer 5

The thyroid produces thyroxine, which regulates metabolic rate, temperature control, heart rate, digestive rate, and the replacement of dead cells in skin and bone, brain development and muscle contraction. It also produces calcitonin, which regulates Ca²⁺ ion concentration in blood.

Question 6

What does adrenaline do in the body?

Answer 6

Adrenaline is produced in the adrenal glands and increases heart rate (heart has adrenaline receptors which can affect the SA node and decelerate depolarisation by increasing Ca2+ current to affect muscle contraction), breathing rate, and alertness, slows digestion, and coordinates the body’s fight or flight response.

Question 7

What is the role of the pancreas in homeostasis?

Answer 7

The pancreas produces insulin and enzymes. Insulin helps regulate blood glucose levels, while enzymes aid in digestion.

Question 8

What is negative feedback in homeostasis?

Answer 8

Negative feedback involves receptors detecting a stimulus, a coordination system transferring information between systems eg nervous or endocrine system, and effectors carrying out a response eg muscle or gland to counteract the stimulus and restore the system to its original level. Factor is continuously monitored and magnitude of correction depends on how much it is deviated from the original.

Question 9

What is positive feedback in homeostasis?

Answer 9

Positive feedback occurs when the original stimulus produces a response that deviates further from normal, enhancing the effect of the original stimulus.

Question 10

What is the process of repairing a broken bone?

Answer 10

Osteoblasts secrete inactive osteocalcin, and osteoclasts secrete acid that activates osteocalcin by causing shape of enzyme to change. Active osteocalcin stimulates insulin release from beta cells in the pancreas by binding to them, and osteoblasts release more inactive osteocalcin as they have insulin receptors. POSITIVE FEEDBACK MECHANISM.

Question 11

What is cell signalling?

Answer 11

Cell signalling coordinates responses to external stimuli. Stimulus is received by receptor cells, transduced into chemical signals, and transmitted to effector target cells via receptors on membrane.

Question 12

What is the difference between paracrine and endocrine cell signalling?

Answer 12

Paracrine signalling involves communication between nearby cells, while endocrine signalling involves hormones acting on distant cells via the circulatory system.

Question 13

What is thermoregulation in humans?

Answer 13

Thermoregulation in humans involves physiological mechanisms to keep body temperature within a narrow range of about 37.5°C, which is optimal for enzyme function as humans are endotherms.

Question 14

How are temperature variations detected in the body?

Answer 14

Changes in external temp detected by peripheral receptors eg skin and mucous membranes and impulses from receptors sent to hypothalamus
Hypothalamus has receptors which can detect temp of blood flowing through it and initiates homeostatic response

Question 15

What is the structure of the skin involved in thermoregulation?

Answer 15

The skin contains sweat glands and pores, free nerve endings (to detect temperature and pain-sensory neuron), hair erector muscles, adipose tissue, capillaries, and arterioles, all contributing to thermoregulation.

Question 16

What is the response to high temperatures?

Answer 16

Responses to high temperatures include vasodilation where muscles in arteriole walls relax (to increase blood flow to the skin capillaries for heat loss by radiation), sweating (to cool the skin by evaporation but ineffective in humid environments as there isn’t a large enough concentration gradient), and the flattening of hairs by hair erector muscles (to allow heat loss through radiation by letting air circulate across skin).

Question 17

What is the response to low temperatures?

Answer 17

Responses to low temperatures include vasoconstriction as muscles in arteriole wall contract (to reduce blood flow to capillaries and redirecting blood to shunt vessels preventing heat loss by radiation), increased metabolic rate to release heat through exothermic reactions (through thyroxine increasing BMR), shivering by repeatedly contracting and relaxing muscles (to generate heat through respiration), and hair erection (to trap insulating air to prevent heat loss by radiation).

Question 18

How does adrenaline affect the body?

Answer 18

Adrenaline binds to specific receptors on the membrane of liver cells
This causes the enzyme adenylyl cyclase to change shape and become activated
Activated adenylyl cyclase catalyses the conversion of ATP to the second messenger molecule cyclic AMP (cAMP)
cAMP binds to protein kinase A enzymes, activating them
Active protein kinase A enzymes initiate a series of enzyme activations that result in the breakdown of glycogen to glucose; this process is known as glycogenolysis
The enzyme cascade described above amplifies the original signal from adrenaline and results in the release of extra glucose by the liver to increase the blood glucose concentration
Also stimulates breakdown of glycogen in muscle cells during excercise

Question 19

What is the role of adrenaline in glycogenolysis?

Answer 19

Adrenaline activates cAMP, which in turn activates protein kinase A enzymes that initiate the breakdown of glycogen into glucose (glycogenolysis), increasing blood glucose.

Question 20

How is blood glucose concentration regulated by negative feedback?

Answer 20

Alpha cells release glucagon when blood glucose is low, triggering glycogenolysis only in liver cells. Beta cells release insulin when glucose is high, increasing glucose uptake by cells and promoting glycogenesis.

Question 21

What is the process of glycogenolysis?

Answer 21

In response to low blood glucose conc. Alpha cells release glucagon and beta cells stop secretion of insulin.
Decrease in insulin levels reduces use of glucose by muscle and liver cells
Glucagon binds to receptors on liver cells membrane causing a conformational change and activating a G protein
Activated G protein activates enzyme adenylyl cyclase which catalyses conversion of ATP to cyclic AMP
cAMP activates protein kinase A by binding causing it to activate phosphorylase kinase enzymes by adding phosphate groups
Phosphorylase kinase enzymes activate glycogen phosphorylase enzymes which catalyse the breakdown of glycogen into glucose which is released into blood

Question 22

What is gluconeogenesis?

Answer 22

Gluconeogenesis is the process by which non-carbohydrate molecules (e.g., lipids) are converted into glucose, which occurs in the liver.

Question 23

What is the cause of Type 1 diabetes?

Answer 23

Type 1 diabetes is caused by an autoimmune response where the T cells attacks beta cells of the islets of Langerhans, preventing insulin production in response to high blood glucose concentrations. Lack of insulin affects glycogen stores leading to fatigue. Dangerously high blood glucose levels can lead to organ damage.

Question 24

What are the characteristics of Type 2 diabetes?

Answer 24

Type 2 diabetes is characterized by reduced insulin sensitivity (reduced number of receptors or they fail to respond in liver and fat storage tissues), leading to decreased glucose uptake and uncontrolled higher blood glucose levels. The beta cells compensate by producing more insulin, but over time, beta cells are damaged.

Question 25

What are risk factors for Type 2 diabetes?

Answer 25

Risk factors for Type 2 diabetes include obesity, physical inactivity, high blood pressure, high blood cholesterol, genetics, and certain ethnic groups.

Question 26

How does poorly controlled diabetes affect blood pressure?

Answer 26

Poorly controlled diabetes leads to high blood glucose, which lowers the water potential of blood, causing more water to move from tissues into blood vessels by osmosis, increasing blood volume and raising blood pressure.

Question 27

What is the function of a colorimeter in urine testing?

Answer 27

A colorimeter is used with a calibration curve and dilutions to calculate the concentration of glucose in urine using Benedict’s solution.

Question 28

What happens during kidney ultrafiltration?

Answer 28

Arterioles branching off renal artery and lead to each nephron, where they form the glomerulus inside Bowman’s capsule
Capillaries get narrower further into glomerulus increasing blood pressure through them (already at high pressure- coming directly from renal artery connected to aorta)
Smaller molecules carried in the blood: forced out of the capillaries into the Bowman’s capsule, where they form filtrate
The blood in the glomerular capillaries is separated from the lumen of the Bowman’s capsule by cell layers with a basement membrane in between them:
The first cell layer is the endothelium of the capillary – each capillary endothelial cell is perforated by membrane-lined circular holes
The next layer is the basement membrane – network of collagen and glycoproteins
The second cell layer: Bowman’s capsule epithelium – these epithelial cells finger-like projections with gaps in between them (podocytes)
Holes in the glomerular capillary endothelial cells + gaps between the podocytes allows substances dissolved in the blood plasma to pass into the Bowman’s capsule
The fluid that filters through from the blood into the Bowman’s capsule = glomerular filtrate
The main substances that pass out of the capillaries and form the glomerular filtrate are: amino acids, water, glucose, urea and inorganic ions (mainly Na+, K+ and Cl-)
Red and white blood cells and platelets remain in the blood as they are too large to pass through the holes in the capillary endothelial cells
The basement membrane acts as a filter as it stops large protein molecules from getting through

Question 29

What is selective reabsorption in the kidney?

Answer 29

Blood capillaries are located very close to the outer surface of the proximal convoluted tubule
As the blood in these capillaries comes straight from the glomerulus, it has very little plasma and has lost much of its water, inorganic ions and other small solutes
The basal membranes (of the proximal convoluted tubule epithelial cells) are the sections of the cell membrane that are closest to the blood capillaries
Sodium-potassium pumps in these basal membranes move sodium ions out of the epithelial cells and into the blood, where they are carried away
This lowers the concentration of sodium ions inside the epithelial cells, causing sodium ions in the filtrate to diffuse down their concentration gradient through the luminal membranes (of the epithelial cells)
These sodium ions do not diffuse freely through the luminal membranes – they must pass through co-transporter proteins in the membrane
There are several types of these co-transporter proteins – each type transports a sodium ion and another solute from the filtrate (eg. glucose or a particular amino acid)
Once inside the epithelial cells these solutes diffuse down their concentration gradients, passing through transport proteins in the basal membranes (of the epithelial cells) into the blood

Question 30

What is the role of aquaporins in osmoregulation?

Answer 30

Aquaporins increase the permeability of the collecting duct to water, allowing water to move from the filtrate to the blood, concentrating urine when water potential of blood is low.

Question 31

What happens during kidney failure?

Answer 31

Urea, water, salts and various toxins are retained and not excreted
Less blood is filtered by the glomerulus, causing the glomerular filtration rate (GFR) to decrease
This leads to a build-up of toxins in the blood
electrolyte balance in the blood is disrupted (the concentrations of ions and charged compounds are not maintained)
Excess potassium ions in the blood can lead to abdominal cramps, tiredness, muscle weakness and even paralysis
If potassium ion concentrations continue to increase, the frequency of impulses from the sinoatrial node in the heart may decrease, potentially leading to arrhythmia and cardiac arrest
Depending on the body’s needs, the kidneys either conserve or secrete sodium, which plays an important role in neuromuscular function, fluid balance and acid/base balance
A build-up of sodium can cause disorientation, muscle spasms, higher blood pressure and general weakness

Question 32

What is hemodialysis?

Answer 32

Partially permeable dialysis membranes separate the patient’s blood from the dialysis fluid (dialysate)
The dialysate contains substances needed in the blood (e.g. glucose and sodium ions) in the right concentrations
As the dialysate contains a glucose concentration equal to a normal blood sugar level, this prevents the net movement of glucose across the membrane as no concentration gradient exists
As the dialysis fluid contains a salt concentration similar to the ideal blood concentration, movement of salts across the membrane only occurs where there is an imbalance
The fluid in the machine is continually refreshed so that concentration gradients are maintained between the dialysis fluids and the blood
Importantly, the dialysate contains no urea: urea diffuses down its concentration gradient from the blood into the dialysate and is eventually disposed of
Countercurrent creating a conc gradient
This means that each time blood circulates through the machine, some more of the urea it contains passes into the dialysate until almost all of it is removed (after approximately 3 hours)
The drug heparin is added to the blood as it is an anticoagulant (blood thinner) that prevents the formation of blood clots

Question 33

What is the purpose of kidney transplants?

Answer 33

Kidney transplants are performed to replace a damaged kidney, but require a compatible blood group and tissue type, as well as immunosuppressants to prevent rejection due to foreign antigens.

Question 34

How are pregnancy tests conducted?

Answer 34

Pregnancy tests use B lymphocyte antibodies specific to the HCG hormone to detect its presence in urine.

Question 35

How are anabolic steroids detected in urine?

Answer 35

Anabolic steroids can be detected in urine using gas chromatography or mass spectrometry.

Question 36

Why are glucose, ketones and proteins detected in urine?

Answer 36

Glucose: if present can suggest issues with insulin eg diabetes
Ketones: acetone produced by metabolism of px with diabetes mellitus
Proteins: blood pressure too high, incorrect protein filtration or kidney infection

Question 37

Describe the process of osmoregulation

Answer 37

Causes luminal membrane of collecting duct to become more permeable to water by increasing no. of aquaporins
Vesicles carrying aquaporins in collecting ducts bind to ADH molecules which causes signalling cascade for phosphorylation of aquaporins
Activated aquaporins fuses with luminal membrane and increases permeability to water
As filtrate travels through collecting ducts water moves from high water potential in collecting duct to low water potential in tissue fluid and blood plasma in medulla
Small volume of concentrated urine produced

Question 38

Which molecules are reabsorbed at the PCT

Answer 38

All glucose in the glomerular filtrate is reabsorbed into the blood
This means no glucose should be present in the urine
Amino acids, vitamins and inorganic ions are reabsorbed
The movement of all these solutes from the proximal convoluted tubule into the capillaries increases the water potential of the filtrate and decreases the water potential of the blood in the capillaries
This creates a steep water potential gradient and causes water to move into the blood by osmosis
A significant amount of urea is reabsorbed too
The concentration of urea in the filtrate is higher than in the capillaries, causing urea to diffuse from the filtrate back into the blood

Question 39

How are water and salts reabsorbed in the kidneys?

Answer 39

As the filtrate drips through the Loop of Henle necessary salts are reabsorbed back into the blood by diffusion
As salts are reabsorbed back into the blood, water follows by osmosis
Water is also reabsorbed from the collecting duct in different amounts depending on how much water the body needs at that time
After the necessary reabsorption of amino acids, water, glucose and inorganic ions is complete, the filtrate eventually leaves the nephron and is now referred to as urine
This urine then flows out of the kidneys, along the ureters and into the bladder, where it is temporarily stored

Question 40

What are the adaptations of the PCT?

Answer 40

Question 41

Why does ultrafiltration occur?

Answer 41

Occurs due to the differences in water potential between the plasma in the glomerular capillaries and the filtrate in the Bowman’s capsule: increased by high pressure and decreased by presence of solutes
Effect of pressure gradient greater than solute gradient- water potential of glomerulus plasma greater than filtrate of Bowman’s capsule- net movement of water from blood into Bowman’s capsule

Question 42

Describe the structure of the kidney

Answer 42

Surrounded by fibrous capsule
Beneath the fibrous capsule:
The cortex (contains the glomerulus, as well as the Bowman’s capsule, proximal convoluted tubule, and distal convoluted tubule of the nephrons)
The medulla (contains the loop of Henle and collecting duct of the nephrons)
The renal pelvis (where the ureter joins the kidney)
Nephron: responsible for the formation of urine
blood vessels associated with each nephron:
Bowman’s capsule of each nephron: glomerulus supplied with blood by an afferent arteriole (which carries blood from the renal artery)
The capillaries of the glomerulus rejoin to form an efferent arteriole + Blood flows into a network of capillaries that run closely alongside the rest of the nephron eventually flows into the renal vein

Question 43

How is type 2 diabetes treated?

Answer 43

Early-stage type II diabetes is typically treated with a sugar- and fat-controlled diet and an exercise regime.
Foods that are rapidly digested into sugar cause dangerous spikes in blood sugar.

Question 44

How is type 1 diabetes treated?

Answer 44

Treatment typically involves regular blood tests, insulin injections (fast/slow acting), and a diabetes-appropriate diet.

Question 45

How do beta cells control blood glucose concentration?

Answer 45

Glucose enters Beta cells by facilitated diffusion and causes increase in ATP due to respiration of excess glucose molecules causing K+ ion channels to close triggering change in membrane potential. CHange in membrane potential causes voltage gated Ca2+ channels to open and insulin secreted in response to influx of Ca2+
Vesicle of insulin to move towards cell membrane and secrete insulin into capillaries to glucose transporter proteins (target cells) and when bound to target cells, stimulates them to activate more glucose transported proteins on cell surface to increase facilitated diffusion of glucose into the cell.
Increases rate of glycogenesis in liver cells: insulin rapidly converted to glucose phosphate in liver cells which use enzymes to convert it into glycogen which lowers glucose conc in liver cells and maintain conc gradient between capillaries

Question 46

What is the structure of adrenal glands?

Answer 46

Outer cortex: produces steroid hormones eg Aldosterone which regulates salt levels in blood and blood pressure + volume. Cortisol which regulates metabolism of respiratory substrates to release usable energy in stress
Central medulla: production of adrenaline which coordinates fight or flight responses

Question 47

What is the purpose of signalling molecules?

Answer 47

SIgnalling molecules are small and easy to transport across cell membrane or may cause changed whilst binding to receptors on outside (proteins/glycoproteins) eg causing enzyme cascade