Chapter 14: Homeostasis Flashcards
1
Q
Homeostasis
A
the maintenance of constant internal environment regardless of changes in external environment
2
Q
Using examples, outline the importance of homeostasis in a mammal
A
- Homeostasis: the maintenance of constant internal environment regardless of changes in external environment.
- The internal environment of an organism refers to all the conditions inside the body.
- Homeostatic mechanisms work by controlling the composition of blood, which therefore controls the composition of the tissue fluid.
- The factor fluctuates around particular ideal value, or set point.
- Temperature - low temperatures slow down metabolic reactions. high temperatures proteins (enzymes) are denatured and cannot function.
- Water potential - if wp decreases, osmosis -> metabolic reactions in the cell slow/ stop, cell shrink. if wp increases, osmosis into the cell -> swell + burst
- Conc. of glucose - glucose is the fuel for respiration -> lack of it = slow down respiration/stop. too much glucose -> osmosis out of cell -> cells shrink.
3
Q
Outline principles of homeostasis with reference to glucose conc
A
- Homeostasis: maintenance of constant internal environment regardless of changes in external environment
- Negative feedback: process in which a change in some parameter, such as blood glucose level, brings about processes which move its level back towards normal again.
- Receptors detect changes in glucose levels
- Alpha cells produces glucagon and beta cells produce insulin in the islets of Langerhans
- Action taken by the effector (liver, muscles)
- Restoration of norm
- Fluctuations around the set point
4
Q
Explain how stimuli, receptors, central control, coordination systems and effectors are involved in maintaining the internal environment of a mammal.
A
- Receptor (or sensor) detects stimuli (any change in a factor, such as a change in blood temperature or the water content of the blood)
- Receptors send information about the changes they detect to a central control through nervous system (input)
- Central control instructs an effector to carry out an action (output)
- Corrective actions: correct changes; continuous adjustments to the output.
- The factor fluctuates around a particular ideal value, or set point.
- Mechanism to keep changes in the factor within narrow limits: negative feedback.
5
Q
Nervous system
A
information in the form of electrical impulses is transmitted along nerve cells (neurones)
6
Q
Endocrine system
A
uses chemical messengers called hormones travel in the blood, in a form of long-distance cell signalling
7
Q
Negative feedback
A
a process in which a change in some parameter, such as blood glucose level, brings about processes which move its level back towards normal again.
8
Q
Excretion
A
The removal of unwanted products of metabolism
9
Q
Excretory products
A
- Carbon dioxide
- respiring aerobically
- transport by bloodstream to the lungs from respiring cells - Urea
- produced in the liver
- produced from excess amino acids
- transported from the liver to the kidneys, in solution in blood plasma.
- Kidneys remove urea from blood and excrete it, dissolved in water as urine.
10
Q
Deamination
A
- In the liver cells, the amino group (-NH2) of an amino acid is removed, together with an extra hydrogen atom.
- Combine to produce ammonia (NH3) and keto acid
- Keto acid: converted to glucose/ glycogen or enter the Krebs cycle and be respired.
11
Q
Ammonia
A
- very soluble and highly toxic compound
- Aquatic animals, ammonia diffuses from the blood and dissolves in the water around the animal.
- Terrestrial animals, ammonia would rapidly build up in the blood and cause immense damage.
- > Damage is prevented by converting ammonia immediately to urea, which is less soluble and less toxic.
12
Q
Urea
A
2NH3 + CO2 -> CO(NH2)2 + H2O (urea)
- the main nitrogenous excretory product
- small quantities of other products: creatinine and uric acid
+ Creatinine: muscles, form of creatine phosphate, energy store.
+ Uric acid: breakdown of purines from nucleotides, not from amino acids
13
Q
Explain why it is important that carbon dioxide and nitrogenous wastes are excreted and not allowed to accumulate in the body
A
- Its conc in the blood would build up and become dangerous.
14
Q
The structure of the kidney
A
- Renal Vein
- Renal Artery
- Afferent arteriole: supply blood to glomerulus by a branch of the renal artery.
- Efferent arteriole: leads off to form a network of capillaries running closely alongside the rest of the nephron. Blood flow into a branch of the renal vein.
- Pelvis: where ureter joins
- thousand of tiny cubes called NEPHRONS
- Bowman’s capsule: a cup-shaped structure
- Glomerulus: tight network of capillaries
- Podocytes: tiny finger-like projections with gaps in between them
- Glomeruli + capsules of all the Nephrons in cortex
- Proximal Convoluted Tubule in Cortex
- Loop of Henle in medulla (descending, ascending): hairpin loop runs deep into the medulla.
- Distal convoluted tubule
- Collecting duct: leads down through the medulla and into the pelvis of the kidney
15
Q
Kidney makes urine in a two-stage process
A
- Ultrafiltration
- Selective reabsorption
16
Q
Ultrafiltration
A
- Reducing blood vessels diameter
- Increases hydrostatic pressure
- 3 barriers:
+ Cappillaries wall-gaps
+ Basement membrane: collagen + glycoproteins
+ Podocytes , gaps between processes - Glomerular filtrate (< 68,000 RMM)
+ Urea
+ Glucose
+ Amino acid
+ Small protein
+ Inorganic ions (Chloride, Sodium, Potassium)
17
Q
Endothelium
A
- first cell layer is the lining of the capillary
- it has gaps, but more gaps in other capillary (each endothelial cell has thousands of tiny holes in it.
18
Q
Epithelial cells
A
- inner lining of the Bowman’s capsule
- these cells have many tiny finger-like projections with gaps in between them, and are called podocytes.
19
Q
Factors affecting glomerular filtration rate
A
- The rate at which the fluid filters from the blood in the glomerular capillaries into the Bowman’s capsule. (human: 125 cm3min-1)
- Differences in WP between the plasma (glomerular capillaries) and filtrate (Bowman’s capsule)
- WP is lowered by the presence of solutes, and raised by HIGH PRESSURES.
- Inside the capillaries (glomerulus), high BLOOD PRESSURE (efferent < afferent) -> raise WP in blood plasma.
- Concentration of solutes in blood plasma > than solutes in the Bowman’s capsule. (protein molecules are too big to get through - 68000 MM) -> WP lower than the filtrate in the Bowman’s capsule.
- Effect of differences in PRESSURE outweighs the effect of differences in solute conc. The WP of the blood plasma > filtrate in the capsule. So water MOVES DOWN the WP gradient from the blood into the capsule.
20
Q
Reabsorption in the proximal convoluted tubule
A
- Selective reabsorption: many of the substances in glomerular filtrate need to be kept in the body
- In proximal convoluted tubule (in cortex)
- lining is made of a single layer of cuboidal epithelial cells
- Adaptation of cuboidal epithelial cells for reabsorption:
+ MICROVILLI: increase the surface area of the inner surface facing the lumen.
+ TIGHT JUNCTIONS: hold adjacent cells together so that fluid cannot pass between the cells, but go through the cells.
+ MANY MITOCHONDRIA: provide energy for sodium - potasium (Na+ - K+) pump proteins in the outer membranes of the cells. - CO-TRANSPORTER PROTEINS in the membrane facing the lumen for sodium to move passively into the tubule down its conc gradient, b
- Process:
1. Basal membrane of PCT use ATP for sodium - potassium pump. DECREASE the conc of sodium ions in the cytoplasm. FOLDED BASAL MEMBRANE gives large surface area for carrier proteins.
2. BLOOD PLASMA absobed Na*, Cl-, glucose and amino acids. This helps further uptake from the lumen of the tubule.
3. Microvilli INCREASE surface area, helping uptake of solutes. Na+ moves passively into the cell down its conc gradient. It moves in using protein co-transporter molecules in the membrane, which bring in glucose and amino acids at the same time. - Urea is reabsorbed too since it is a small molecule which passes easily through cell membranes.Its conc in the filtrate is considerably higher than that in the capillaries, so it diffuses passively into the blood.
- Other two nitrogenous excretory products: uric acid and creatinine: actively secreted by the cells of the proximal tubule into its lumen, not reabsorbed.
-> reduces the V of liquid remaining. In adult, 125cm3min-1 enter PCT, only 64% passes on to the loop of Henle.
21
Q
Reabsorption in the loop of Henle and collecting duct
A
- loop of Henle in medulla
- Allows production of very concentrated urine, water is conserved in the body, helping to prevent DEHYDRATION.
- Descending loop of Henle: permeable to Na+ and water
- Ascending loop of Henle: permeable to Na+ and impermeable to water
- The longer the loop, the more concentrated the fluid inside the loop.
1. Na+ and Cl- are actively transported out of the ascending limb.
2. This raises the conc of Na+ and cl- in the tissue fluid.
3. This in turn causes the loss of water from the descending limb
4. The loss of water concentrates Na+ and Cl- in the descending limb
5. Na+ and Cl- ions diffuse out of this concentrated solution in the lower part of the ascending limb. - > Counter-current mechanism in the loop of Henle builds up high conc of Sodium ions and Chloride ions in the tissue fluid of the medulla.
22
Q
Reabsorption in the loop of Henle and collecting duct
A
- loop of Henle in medulla
- Allows production of very concentrated urine, water is conserved in the body, helping to prevent DEHYDRATION.
- Descending loop of Henle: permeable to Na+ and water
- Ascending loop of Henle: permeable to Na+ and impermeable to water
- The longer the loop, the more concentrated the fluid inside the loop.
1. Na+ and Cl- are actively transported out of the ascending limb.
2. Raises the conc of Na+ and cl- in the tissue fluid.
3. Loss of water from the descending limb
4. Concentrates Na+ and Cl- in the descending limb
5. Na+ and Cl- ions diffuse out of this concentrated solution in the lower part of the ascending limb. - > Counter-current mechanism in the loop of Henle builds up high conc of Sodium ions and Chloride ions in the tissue fluid of the medulla.
23
Q
Ability of some small mammals (rodents) produce very concentrated urine
A
- Related to the relative thickness of the medulla in their kidneys.
- Large medulla
- Deep infolds with many Na+ - K+ pump in ascending loops of Henly
- Many mitochondria with many cristae in cytoplasm, production of ATP -> energy for the pumping of sodium ions into the tissue fluid.
24
Q
Reabsorption in the distal convoluted tubule and collecting duct
A
- First part of distal convoluted tubule functions - same way as the ascending limb of the loop of Henle.
- 2nd part fuction = same way as the collecting duct
- In the distal convoluted tubule and collecting duct, Sodium ions (Na+) are actively pumped from the fluid in the tubule into the tissue fluid, from where they pass into the blood.
- Potassium ions (K+)
25
Q
Reabsorption in the distal convoluted tubule and collecting duct
A
- First part of distal convoluted tubule functions - same way as the ascending limb of the loop of Henle.
- The cells of the ascending limb of the loop of Henle and the cells lining of the collecting ducts are permeable to urea, which diffuses into the tissue fluid.
- > Urea is also concentrated in the tissue fluid in the medulla.
- Therefore, fluid passes once again through the regions where the solute concentration of the tissue fluid is very high and the WP is very low.
- > Water can move out of the collecting duct, by osmosis, until the WP of urine is the same as the WP of tissue fluid in the medulla.
- 2nd part fuction = same way as the collecting duct
- In the distal convoluted tubule and collecting duct, Sodium ions (Na+) are actively pumped from the fluid in the tubule into the tissue fluid, from where they pass into the blood.
- Potassium ions (K+) are actively transported INTO the tubule.
- The rate at which these two ions are moved into and out of the fluid in the nephron can be varied.
- > Helps to regulate the concentration of these ions in the blood.
26
Q
Osmoregulation
A
the control of the water potential of body fluid. This regulation is an important part of homeostasis and involves the hypothalamus, posterior pituitary gland and the kidneys.
27
Q
Osmoregulation
A
the control of the water potential of body fluid. This regulation is an important part of homeostasis and involves the hypothalamus, posterior pituitary gland and the kidneys.
