Homeostasis Flashcards
1
Q
What is homeostasis?
A
- the maintenance of a relatively constant internal environment for the cells within the body
2
Q
What factors are controlled by homeostasis?
A
- core body temp.
- metabolic wastes; carbon dioxide and urea
- blood pH
- blood glucose conc.
- water potential of blood
- oxygen and carbon dioxide conc.
3
Q
What two systems control homeostasis?
A
- Endocrine system
- Nervous system
4
Q
What are four features of tissue fluid that influence cell activities?
A
-
temperature:
low temperatures slow down metabolic reactions
high temperatures denatures enzymes and proteins -
water potential:
if w.p decreases, water moves out of cell, so metabolic reactions slow/stop
if w.p increases water may enter cell by osmosis and cause it to burst -
conc. of glucose in blood:
low glucose; respiration slows down
high glucose; can cause water to move out of cell -
pH:
controls enzyme activity
5
Q
What is negative feedback?
A
- a process in which some change in parameter (e.g blood glucose conc.) brings about a process which returns it to normal
6
Q
Describe negative feedback mechanism:
A
stimuli –> receptor –> CNS/brain –> effector –> response
e.g; thermoregulation
stimuli: increase in core body temp.
response: vasodilation/sweating to reduce body temp.
7
Q
What is positive feedback?
A
- when a change in parameter brings about a process that further moves the change in its initial direction
e.g; if something increases, it will increase more
8
Q
What is excretion?
A
- the removal of toxic/waste products of metabolism from the body
9
Q
What are two excretory products?
A
- Carbon dioxide
- Urea
10
Q
What is deamination?
A
- the breakdown of excess amino acids in the liver by the removal of an amine group
- amino acid –> keto acid + ammonia
- ammonia will be converted into urea
11
Q
What happens to a keto acid?
A
- it is respired or converted into glucose, glycogen or fat and can enter Krebs cycle
12
Q
Why is ammonia converted into urea?
A
- ammonia is:
- very soluble
- highly toxic
- increases pH in cytoplasm
- can interrupt respiration and cell signaling
13
Q
How is ammonia converted into urea?
A
2NH3 + CO2 –> CO(NH2)2 + H2O
ammonia + carbon dioxide –> urea + water
- urea is less soluble and less toxic than ammonia
14
Q
What are the main components of the excretory system?
A
- inferior vena cava + aorta
- kidneys
- renal vein + artery
- ureter
- bladder
- urethra
15
Q
What are the main components of a Kidney?
A
- Fibrous capsule
- Cortex
- Medulla
- Nephron
- Branches of renal vein + artery
- Pelvis
- Ureter
16
Q
What are the components of a Nephron?
A
- Bowman’s capsule + glomerulus
- Proximal convoluted tubule
- Loop of Henlé
- Distal convoluted tubule
- Collecting duct
17
Q
What parts of the nephron are located in the cortex?
A
- Bowmans capsule + glomerulus
- PCT
- DCT
18
Q
Which parts of the nephron are located in the medulla?
A
- loop of Henlé
- collecting duct
19
Q
What is the process of ultrafiltration?
A
- occurs in Bowman’s capsule
- blood flows from renal artery in AFFERENT arteriole
- small molecules (amino acids, glucose, water, urea) are filtered out of the blood capillaries of glomerulus
- into the Bowman’s capsule to form glomerular filtrate
- large molecules such as plasma proteins cannot pass through basement membrane
20
Q
What are the afferent and efferent arterioles?
A
Afferent: leads towards the glomerulus
Efferent: leads away from the glomerulus
21
Q
How many layers are between the capillaries and the lumen of the Bowman’s capsule?
A
- Three layers;
- endothelium of capillary
- basement membrane
- Bowman’s capsule epithelium (consists of podocytes)
22
Q
Factors that effect water potential in the Bowman’s capsule + glomerulus:
A
Pressure:
- afferent arteriole wider than efferent, so blood pressure in glomerulus is HIGH
- so w.p in glomerulus higher
- so water moves by osmosis into the Bowman’s capsule
Solute Concentration:
- since plasma proteins, RBC, WBC’s and platelets cannot enter through basement membrane
- solute concentration in glomerulus is HIGH
- so water moves by osmosis into the glomerulus
- Pressure outweighs solute concentration, so net movement of water is out of glomerulus, into the Bowman’s capsule
23
Q
What is selective reabsorption?
A
- movement of certain substances from the filtrate in the nephrons back into the blood
24
Q
What substances are reabsorbed in the PCT?
A
- ALL glucose, by active transport
- amino acids, inorganic ions, vitamins
- water moves into blood by osmosis
- urea
25
What is the process of selective reabsorption in the PCT?
- **basal membranes** in PCT have **sodium-potassium pumps**
- **Na+ is pumped out of the PCT cells**, using ATP, into the blood
- by **active transport**
- so Na+ diffuses back into PCT from **lumen** since concentration gradient forms
- glucose, amino acids and Na+ move into the PCT through a **co-transport mechanism**
- through **carrier/transport protein**
- glucose and amino acids can diffuse back into the blood
- _ALL_ glucose reabsorbed into blood
- _SOME_ water and urea reabsorbed
26
What are the adaptations of the PCT for selective reabsorption?
- Many **microvilli**; increases SA
- Many **co-transporter proteins** in **luminal membrane**; each co-transporter moves a specific solute (e.g; glucose)
- Many **mitochondria**; provide energy for sodium-potassium pumps in basal membranes
- Cells **tightly packed together**; no fluid can pass between cells
- folded basal membrane for **many** sodium pumps
27
What is reabsorbed in the loop of Henlé?
- **salts** are reabsorbed at ascending limb FIRST
- water potential in loop gets higher so;
- **water** reabsorbed at descending limb by osmosis
28
What is reabsorbed at the DCT and collecting duct?
- the first part of the DCT functions like the loop of Henle, whereas the second part of the DCT functions like the collecting duct
- in the collecting duct, **sodium** ions are actively pumped **OUT** the tubule to blood
- **potassium** ions are actively transported **IN** the tubule
29
What is osmoregulation?
- the **control of water potential** of blood and tissue fluid
- by controlling water concentration or ion content
30
What happens if the water potential of the blood is LOW?
- **osmoreceptors** in **hypothalamus** are stimulated
- nerve impulse sent to **posterior pituitary gland**
- **ADH released**
- ADH binds to receptors on membrane of collecting duct
- **enzyme cascade** signaled by cAMP
- vesicles with aquaporins move towards membrane
- number of **aquaporins** on luminal membrane of collecting duct INCREASE
- collecting **ducts become more permeable** to water
- filtrate flows along CD and water moves into blood
- **concentrated urine** produced
- flows of the kidney through ureter and into bladder
31
What happens if the water potential of the blood is too HIGH?
- **Osmoreceptors in the hypothalamus** are not stimulated
- No nerve impulses are sent to the posterior pituitary gland
- **No ADH released**
- **Aquaporins are moved out** of the luminal membranes of the collecting duct cells via vesicles
- Collecting duct cells are **no longer permeable** to water
- The filtrate flows along collecting duct but loses no water and is very dilute
- A large volume of **dilute urine** is produced
- This flows from the kidneys, through the ureters and into the bladder
- w.p in blood decreases
32
Describe the action of ADH on the kidney:
- affects collecting duct
- **binds to receptors on cell surface membrane** of collecting duct
- **activates series of enzyme controlled reactions**
- final enzyme produced is **phosphorylase**
- aquaporins/**vesicles move to cell surface** on luminal side
- aquaporins **fuse with cell surface membrane**
- cells become **more permeable** to water
- water moves out of lumen
- **down water potential gradient**
- into bloodstream
33
What do a-cells secrete?
Glucagon
34
What do B-cells secrete?
Insulin
35
What happens when there is an increase in blood glucose?
- glucose enters B-cells by **facilitated diffusion**
- these cells respire and **produce ATP**
- **potassium channels close**
- **voltage-gated calcium channels open**
- **Insulin secreted** by exocytosis
- insulin binds to receptors on liver, muscle and adipose tissue
- **permeability** of target cells to glucose increases
- insulin activates **glucokinase enzyme**
- which phosphorylates glucose to keep it **inside target cells**
- **glycogen synthase**
- catalyses **glycogenesis**
36
How is blood glucose regulated?
To decrease:
- **glycogenesis**
- increased **uptake of glucose** by cells
- increased use of glucose in **respiration**
To increase:
- **glycogenolysis**
37
What three enzymes does insulin activate?
- **glucose kinase**; phosphorylates glucose to keep it inside target cells
For glycogenesis; synthesis of glycogen by addition of glucose monomers
- **phosphofructosekinase**
- **glycogen synthase**
38
What happens if there is a decrease in blood glucose?
- Pancreatic a-cells secrete **glucagon**
- Glucagon binds to liver cell receptors
- Conformational change to receptor activates **G protein**
- G protein activates **adenylyl cyclase**
- Adenylyl cyclase uses ATP to make **cAMP**
- cAMP binds to **protein kinase A** enzymes
- protein kinase A activate **phosphorylase kinase** enzymes
- phosphorylase kinase activates **glycogen phosphorylase** enzymes
- **Glycogenolysis** occurs
- blood glucose conc. increases
39
How is the concentration of glucose measured in urine?
- glucose presence in urine may indicate diabetes
- **test strips**
- contain **glucose oxidase and peroxidase**
reactions:
by glucose oxidase
- glucose + oxygen ----> gluconic acid + hydrogen peroxide
by peroxidase
- hydrogen peroxide + chromogen (colourless) ----> oxidized chromogen (coloured) + water
40
How is glucose measured in the blood?
- **biosensors**
- a device that uses biological material such as an enzyme to measure the concentration of a chemical compound
- uses glucose oxidase immobilized on a recognition layer
41
Describe the structure of a guard cell:
- thick cell wall facing stoma and thick waxy cuticle
- cellulose microfibrils arranged in bands around cell
- cell walls have no plasmodesmata
- folded cell surface membrane and contains many channel proteins
- cytoplasm contains chloroplasts + mitochondria
- chloroplast have thylakoids, few grana
- many cristae in mitochondria
- several small vacuoles
- nucleus
42
What causes stomata to open and why do they need to open?
*what*
- increase light intensity
- low CO2 conc. in leaf
*why*
- to gain CO2 for photosynthesis
- allow O2 out
- allow transpiration stream to occur which
- brings water/mineral ions in
- for photosynthesis/turgidity
43
What causes stomata to close and why do thy need to close?
*what*
- in darkness
- in low humidity/high temperature/water stress/high wind
*why*
- CO2 not needed for photosynthesis
- to maintain cell turgidity/prevent water loss
44
Explain the mechanism by which guard cells open stomata:
- **proton pumps** in cell surface membrane
- actively pump **H+ out of cell**
- lower H+ conc inside
- **K+ channels open**
- K+ moves into cell by **_facilitated_ diffusion**
- **Cl-** ions enter cell
- **water potential** of cell **decreases**
- water moves in by **osmosis**
- aquaporins
- volume of guard cell increases and becomes more **turgid**
45
Describe the role of abscisic acid (ABA) in stomata closure:
- ABA is a **stress hormone**
- plant secretes ABA in **high temp./dry conditions**
- ABA binds to **receptors**
- on cell surface membrane of guard cells
- **inhibits proton pumps**
- **high H+ conc.** in cell
- ABA stimulates Ca2+ into cell
- allowing **K+ to diffuse out of cell**
- water potential in cell **increases**
- water moves out by **osmosis**
- volume of guard cells decrease and they become **flaccid**
- quick response
46
Explain the reabsorption of water in loop of Henlé:
- sodium ions are reabsorbed in the descending limb/less Na in filtrate
- this is done by Na+ being actively pumped from filtrate into tissue fluid in medulla (then passes to blood)
- this increases the water potential of the filtrate
- so more water is reabsorbed by osmosis
- decreases volume of urine
