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Flashcards in Homeostasis Deck (84):

What is Homeostasis?

The maintenance of a constant internal environment despite changes in the external environment


Why is keeping your internal environment stable so important?

It is vital for cells to function normally and to stop them being damaged


What three things need to be maintained to ensure optimum conditions for a cell to function correctly?

1. Blood pH
2. Core temperature
3. Glucose concentration


What pH level is optimum?



What core temperature is optimum?

37 degrees


Why did pH and Core temperature need to be controlled?

As they both affect enzyme activity and enzymes control the rate of metabolic reactions. If incorrect, enzymes may become denatured.


Why does Blood glucose need to be maintained?

As cells need glucose for respiration to release energy and it can affect the water potential of blood


What blood glucose level is optimum?

5 mmol dm-3


Explain why a HIGH blood glucose concentration (aka. hyperglycemia) is potentially dangerous

- As it lowers the water potential of the blood
- Water moves into blood by Osmosis.
- This leads to blood volume increasing
- Blood pressure increases and dehydration of important organs occurs (e.g. the brain)
- A high conc can be due to lack of INSULIN or insulin resistance/don't respond to insulin


Where can glucose come from?

Diet - hydrolysis of carbohydrates such as starch
Hydrolysis of Glycogen (glycogenolysis)
Gluconeogenesis - glucose from amino acids


The biggest effect of having a low blood glucose concentration (hypoglycemia)?

Lack of glucose for respiration (aerobic) and water potential increases so lowers blood pressure as water leaves the blood via Osmosis


A mechanism that restores a level back to normal in a system

Negative feedback


EQUATION: How can you calculate the pH of a solution?

pH = - log10 [H+]


The likelihood of water molecules to diffuse out or into a solution

Water potential


Which physiological variables does the Negative Feedback mechanism provide stability for?

1. Blood pH
2. Water Potential
3. Glucose concentration
4. Core temperature


What is the Negative Feedback 'loop'?

Normal level > level changes from normal > Receptors detect change > Communication via nervous or hormonal system > Effectors respond > Level brought back to normal


What is the detector of the physiological variables in the brain?

The hypothalamus


What are effectors?

give E.g's

Muscle/glands that cause a response

Temperature change
Adrenaline which increase metabolic rate
Shivering - contraction of muscles
Vasoconstriction/dilation of arterioles
Sweat Glands (evaporation of water)
Behavioural Response - put more clothes on if cold etc.


What is Positive Feedback?

When effectors respond to further increase the level away from the normal level - a change away from normal.
It is useful to rapidly activate processes in the body


Where is blood glucose concentration monitored?



When would blood glucose automatically rise and fall?

Rise = after eating carbohydrate food
Fall = after exercise as its used in respiration


Why is gluconeogensis (breaking down amino acids) the last resort for sourcing glucose?

As proteins cannot be stored so you are essentially breaking down the muscle (e.g. why anorexic people are skinny)


A structure of the pancreas that contains receptors that are sensitive to blood glucose concentration

Islets of Langerhans


Name the two types of Islet cells that control blood glucose?

Alpha cells ( a-cells)
Beta cells (b-cells)


An islet cell that when production of glucose is low, there is production of glucagon to raise it

Alpha cells (a-cells)


An islet cell when glucose levels are high, there is production of insulin to lower it

Beta cells (b-cells)


Hormones, such as insulin and glucagon, only bind to cells with what?

Specific receptors (e.g. target cells)


'genesis' means...



'lysis' means...



'neo' means...



Where are hormones produced?

By Endocrine glands


What happens after a meal high in carbohydrates?

1. Blood glucose increases above normal
2. Detected by Beta cells
3. Secrete insulin
4. which is released into the blood and travels to target cells - mainly the liver and muscle cells
5. Insulin binds to specific receptors on the target cell membrane
6. Causes a reduction in blood glucose concentrations


How does insulin reduce blood glucose? (Beta)

1. Insulin activates enzymes which convert glucose to glycogen (glycogenesis)
2. Insulin activities enzymes to convert glucose to fats
3. Increasing respiration rates in cells > use glucose


How does glucagon increase blood glucose? (Alpha)

1. Glucagon activates enzymes which convert glycogen to glucose (glycogenolysis)
2. Glucagon stimulates conversion of amino acids and glycerol to glucose (gluconeogenesis)


What is the role of adrenaline?

It is secreted from the adrenal glands when glucose is low in the blood


How does adrenaline work?

1. Adrenaline attaches to receptor site on liver cell
2. This activates the enzyme adenylate cyclase inside the membrane
3. The enzyme converts ATP to cyclic AMP (aka. cAMP) which acts as a second messenger
4. This activates the enzyme protein kinase A
5. causing a chain of reactions that break down: glycogen >>> glucose (glycogenolysis)


The enzyme converts ATP to cyclic AMP (aka. cAMP)

Adenylate Cyclase


Why can insulin not be given orally in tablet form?

As it is a protein and so will be hydrolysed in the stomach and small intestine by Protease


A type of diabetes that causes the inability to produce insulin and the body's own immune system may destroy the B-cells (an autoimmune response)

Type I (1) diabetes


How can people with Type I diabetes be treated?

Injection of insulin in proportion to the amount of glucose intake


A type of diabetes that is caused by a loss of responsiveness of target cells to insulin due to receptor abnormalities and is often linked with obesity

Type II (2) diabetes


How can Type II diabetes be managed?

By careful regulation of diet, especially sugar intake and balancing with the amount of exercise done by person.


What recommendations might health advisers make tot the public to reduce the incidence of diabetes?

-Eat a low in fat diet and sugar to lower calorie intake
-Take regular exercise to increase energy expenditure
-Lose weight
^ to all reduce the risk of obesity


How might food and drink manufacturers attempt to make their products healthy?

-Reduce portion sizes
-Use low calorie sweeteners
-Reduce sugar, salt and fat content of food


Why might food and rink manufacturers be reluctant to make their products healthier?

-alter the taste - customers may not like it
-many customers do not want to be forced the healthy option
-may decrease profits


What are the two main functions of the kidneys?

1. Excretion - filtration of waste from blood (e./g urea/CO2)


An organ is found in the lower back of abdominal cavity where urine is formed and then is passed to the bladder for storage

The Kidney


What are the three main regions of the kidney?

1. The outer cortex
2. The medulla
3. The pelvis


This structure is the functional unit of the kidney and each kidney is made up with about one million of them. each one is 14 mm long and is surrounded by a bunch of capillaries



If glucose was not reabsorbed and went into urine what would this show a sign of?

A person with Type I diabetes


The longer the Loop of Henle...

the more concentrated urine


Why is the afferent arteriole wider than the efferent arteriole?

As a bigger build up of high hydrostatic pressure is needed to push the solution out


What is the function of the Renal capsule?

To filter blood arriving in the arteriole from the renal artery


Within the Bowman's capsule is a knot of blood capillaries called the...



Bowman's Capsule + Glomerulus =

Renal Capsule


Where does urine go from the collecting duct?

It passes through the pelvis of the kidney, to the ureter and finally to the bladder


What are the cells that line the inside of the Bowman's Capsule called?



Write a summary describing the pathway a water molecule would take passing from the lumen of a capillary (glomerulus) to the lumen of the Bowman's capsule - ultrafiltration

1. Endothelium of the capillary through a pore
2. Through the basement membrane
3. Through gaps in the Podocytes
4. Filtered into lumen in Bowman's Capsule


Which components of blood are not found in the filtrate in the Bowman's Capsule and why?

- Blood plasma, large proteins, platelets, blood cells
as they are too large to pass through pores of the capillary endothelium/the membrane


State three things that may be found in the filtrate?

Amino acids, water, solutes (e.g. glucose, urea)


How is the Glomerulus adapted to its function?

Pores to allow small molecules to pass through


How is the Bowman's Capsule adapted to its function?

Podocytes wrap around capillaries and combine to create filtration slits/gaps


What happens to most of the filtrate?

It is reabsorbed into the blood


Proteins in urine indicate...

kidney failure


Where does Selective Reabsorption take place?

In the Proximal Convoluted Tube


How is the Proximal Convoluted Tube adapted to its function?

Microvilli - large SA for diffusion
Many Mitochondria - produce ATP for Active Transport


Describe how glucose is reabsorbed from the filtrate in the PCT

1. Glucose enters PCT via facilitated diffusion through specific co-transport proteins with Na+
2. Due to low glucose concentration in capillaries branching from the efferent arteriole (leaving Bowman's Capsule), glucose diffuses into blood
3. Active Transport is involved as Na+ is taken into the blood with glucose


Reabsorption of glucose causes a ........................... in water potential so water enters PCT cells by...........................from the filtrate

Water Potential


The concentration of the blood and the filtrate in the PCT is 300 units. What happens to the concentration of filtrate as it flows down the descending limb?

The concentration increases to 600 units then 1000 units as less water is leaving the descending limb by osmosis


What happens to concentration of tissue fluid with increasing depth into the medulla?

Increases with depth = deeper means more salts come out


What happens to the concentration of filtrate as it flows up the ascending limb?

The concentration decreases as more Na+ and Cl- are being actively transported out of the ascending limb into the middle tissue fluid/medulla


What is the purpose of the maintenance of sodium ions in the medulla and loop of Henle?

The action of the loop of Henle creates a gradient of sodium ions in the medulla, which allows water to be reabsorbed from the collecting duct


The loop of Henle is known as a......

countercurrent multiplier: as the fluid flows in opposite directions in the two sides of the loop (up and down)


What is the overall function of the loop Henle?

To create a region of Na+/salt concentration, and therefore a lower water potential - dry conditions so animals can conserve water


The homeostatic mechanism that controls the water potential of the blood



A peptide hormone synthesized in the hypothalamus and stored in the posterior pituitary to be released into the bloodstream



Give three ways in which water can be lost from the body



Osmoreceptors detect...

a decrease in water potential in the blood and send nerve impulses to the posterior pituitary glands where ADH is stimulated


How does ADH increase the permeability of the collecting duct (DCT) cells in the kidney to water?

It increases transcription and insertion of aquaporin's into the membrane of these cells


What are aquaporin's?

Protein water channels that allow water molecules to move down their water potential gradient > into the medulla > blood capillaries (vasa recta)


Suggest three symptoms you would expect in a person with a lack of ADH?

- Dehydration
-Lots of dilute urine
- Mineral ion imbalance
-Large volume of urine


Coffee inhibits release of ADH, how would this effect the amount of water reabsorbed into the blood?

ADH is needed to increase permeability of the collecting duct to water through the use of aquaporin's. Without ADH, less water will be reabsorbed


Why is it important for someone being tested for diabetes/blood glucose levels to not eat eight hours before the test?

To restore normal blood glucose concentrations


Suggest an explanation for a person having a high value for the fasting blood glucose test?

May have had a drink containing sugar beforehand causing a spike