Homeostasis Flashcards
Define homeostasis
Maintenance of constant internal environment
Keep set points stable within narrow limits in the body
Irrespective of the changes in external environment
Negative feed back mechanism
Stimulus (refers to internal or external change in factors away from norm)
Receptors (cells/ tissue/organ which detect the stimulus)
Control Centre
effectors
Response (corrective)
negative feedback is the mechanism when there is a change and the body responds b counteracting the change
Deamination
Remove amine group and H atom from amino acid
Produce ammonia (toxic if allowed to accumulate)
Urea cycle (ornithine cycle)
NH3 + CO2 —> urea (excreted by kidneys)
Ketonacid remains —> respired or converted to glucose
Nephron structure
a structure that produces urine made of bowman’s capsule and tubules
[cortex]
1. renal artery (afferent–efferent arterioles) 2. at the bowman’s capsule.
3. Proximal convoluted tubule (PCT)
5. Distal convoluted tubule (DCT)
6. Collecting duct
[medulla]
4. Loop of Henle
6. extended collecting duct
[pelvis]
6. end of collecting duct
how is the high pressure in glomerulus generated?
Diameter of the Afferent arteriole > diameter of the Efferent arteriole
forcing substance our with the high-pressure
Filters present
tiny gaps between the endothelium walls of the capillary prevent RBC
Basement membrane prevents large proteins from leaking through
Podocytes are inner bowman’s capsule wall which has gaps for filtrate to leak through
[selective reabsorption]
PCT reabsorbs all glucose and amino acids, most water ad some salts with urea.
Loop of Henle reabsorbs some H2O, salt and urea.
Collecting duct reabsorbs some water.
selective reabsorption in PCT
Na+/K+ pump actively pumps Na+ into the capillaries by ATP
creates a Na+ gradient between PCT lumen and cells
co-transport of Na+/glucose and Na+/a.a into the cells
Glucose and move into blood by facilitated diffusion
Increased H2O potential of PCT lumen causes H2Oto be reabsorbed by osmosis Urea also passively reabsorbed
basal membrane always facing the capillary
Osmoregulation
the control of water potential in the blood and tissue fluid
How is blood H2O potential regulated
[stimulus]
Blood vessel’s H2O potential changes
[receptors]
detected by osmoreceptors in the hypothalamus (brain)
[Control Centre]
Neuron send a signal to the posterior pituitary gland (brain)
[Effectors]
To release or not to release ADH ?
What is ADH?
Anti Diuretic Hormone
a hormone in the body that reduces urine production
With more ADH more H2O is reabsorbed as the collecting duct becomes more permeable to water
therefore less volume of urine with high in conc is produces
With less ADH less H2O is reabsorbed as the collecting duct is now less permeable to to water
therefore high volume of urine produced with a low conc.
How does ADH affect collecting duct permeability/
ADH binds to a receptor on the cell surface membrane of collecting duct cells
begin a cascade reaction to produce active phosphorylase
vesicles with aquaporin fuse within the surface membrane
collecting duct is now more permeable to water
why does the body regulate Blood glucose conc.
[If glucose received by the cell is low]
Less respiration
Les ATP is produced
muscle cells cannot contract (improper function)
[If glucose received by the cell is high]
Because water potential in the cell is very low causing flaccid cell and eventually lead to cell death by osmosis
How does the body regulate Blood glucose conc.
[Stimulus]
change in conc of glucose in blood
[receptors]
Islets of Langerhans located in the pancreases
[control cenre]
Islets of Langerhans located in the pancreases
α cells: secrete less glucagon
β cells: secrete more insulin
[effector]
liver and/or skeletal muscles
how does blood glucose conc. maintained when increased in liver cell
facilitated diffusion through the membrane proteins
GLUT proteins
When glucose molecules enter the cell wither by liver or skeletal muscle cells they create a gradient that may cause glucose to diffuse back out through the proteins
Membrane with GLUT allow glucose to enter by FD
Phosphorylated by glucokinase to prevent diffusing out
Increasing respiration and ATP formation
activates glycogen synthase
correction task: lowering the blood glucose conc.
how does blood glucose conc. maintained when increased in skeletal cell
Vesicles diffuse within the cell surface membrane first then GLUT is on the membrane
Membrane with GLUT allow glucose to enter by FD
Phosphorylated by glucokinase to prevent diffusing out
Increasing respiration and ATP formation
activates glycogen synthase
correction task: lowering the blood glucose conc.
GLUT PROTEIN
GLU: glucose
T: transport
In liver cell
always permeable
present on cell surface membrane
In skeletal muscle
Not always on the surface membrane
How does Glucagon increase blood glucose conc.
adrenaline/Glucagon binds to receptors in the cell surface membranes of liver cells
This binding causes a conformational change in the receptor protein that activates a G protein
This activated G protein activates the enzyme adenylyl cyclase
Active adenylyl cyclase catalyses the conversion of ATP to the second messenger, cyclic AMP (cAMP)
cAMP binds to protein kinase A enzymes, activating them
Active protein kinase A enzymes activate phosphorylase kinase enzymes by adding phosphate groups to them (phosphorylation)
Active phosphorylase kinase enzymes activate glycogen phosphorylase enzymes
Active glycogen phosphorylase enzymes catalyses the breakdown of glycogen to glucose
This process is known as glycogenolysis
Measuring Glucose conc. in the urine using test strip
Test strip
Immobilized enzyme
(Glucose oxidase and peroxidase)
The pad is immersed in the urine sample for a short time
If glucose is present:
Glucose oxidase catalyses a reaction in which glucose is oxidised to form gluconic acid and hydrogen peroxide
Peroxidase then catalyses a reaction between the hydrogen peroxide and a colorless chemical in the pad to form a brown compound and water
Urine tests only show whether or not the blood glucose concentration was above the renal threshold whilst urine was collecting in the bladder – they do not indicate the current blood glucose concentration
Measuring Glucose conc. in the urine using Biosensors
A biosensor can be used by people with diabetes to show their current blood glucose concentration
a biosensor uses glucose oxidase (but no peroxidase) immobilised on a recognition layer
Covering the recognition layer is a partially permeable membrane that only allows small molecules from the blood to reach the immobilised enzymes
When a small sample of blood is tested, glucose oxidase catalyses a reaction in which any glucose in the blood sample is oxidised to form gluconic acid and hydrogen peroxide
The hydrogen peroxide produced is oxidised at an electrode that detects electron transfers
The electron flow is proportional to the glucose concentration of the blood sample
The biosensor amplifies the current, which is then read by a processor to produce a digital reading for blood glucose concentration
This process is complete within a matter of seconds
Function of stomata
allows gas exchange in plant leaf and transpiration
Opening of Stomata conditions
high light intensity
closing of stomata conditions
low light intensity
very low humidity
high temperatures
How do guard cells open and close
Water entering by osmosis and becoming turgid and stomata opens
all walls nearer to the pore is thicker
cell wall further from the pore is thinner
(uneven cell thickness)
cell walls joined together
causes a larger opening
the outer walls are more able to stretch and cause the uneven cell wall thickness
increasing length
