Homeostasis Flashcards
(44 cards)
Define homeostasis
Homeostasis=maintenance of constant internal environment
Keep set point stable within narrow limits in body
Irrespective of changes in external environment
*Factors such as temperature, water potential, glucose concentration must be maintained in the tissues fluid because it affects cell function
*So that internal environment can:
➡️Be stable
➡️Function optimally
*Control systems often work by using a negative feedback mechanism
What is negative feedback and what are the components needed for negative feedback?
Components needed:
*Stimulus
*Receptor
*Control center
*Effector
*Response
➡️Restoration of norm or set point
*Continuous monitoring of the factor affecting the internal environment
*Resulting in many “corrective actions”
*Factors thus fluctuates around the norm/set point stable
What is a stimulus?
Stimulus refers to internal or external change in factor away from norm/set-point
What is a receptor?
Cells/tissue/organ which detect the stimulus
What is a coordinating centre?
Consists of tissue which receives and processes messages, in the form of hormones or nerve impulses from the receptors and determines the appropriate response.
Only if the stimulus reaches a certain threshold/is strong enough, it sends messages to an effector.
What is an effector?
Tissues/organs which receive messages from coordinating centre and carry out a corrective reaction.
What is a response?
The reaction carried out by the effectors.
In negative feedback response counteract the stimulus. Return to set point/ norm
Compare positive vs negative feedback response
Positive feedback:
*Response reinforce the original stimulus
*Very uncommon
*Response worsen/intensifies the initial change
E.g. Labour pains, ripening of fruit, inhalation of CO2
Negative feedback:
*Response counteracts the original stimulus
*Common in the body
*To maintain homeostasis/stable internal environment
E.g. maintaining blood glucose levels, temperature,oxygen levels, water content in blood etc
What is excretion
Removal of unwanted products of metabolism
→Toxic,poisonous, will cause damage to tissues
Main excretory products:
a)Carbon dioxide
→From aerobic respiration
→Excreted via bloodstream and lungs
b)Urea (nitrogenous waste)
→Produced in liver
→From excess amino acids
→Excreted via kidneys
c)Creatinine (Nitrogenous waste)
→Small amounts produced in liver
→From certain amino acids
→Most used as energy storage in muscles
→Excreted via kidneys
d)Uric acid (Nitrogenous waste)
→Produced in liver
→From excess purines of nucleotides
→Excreted via kidneys
Describe Urea
*Main nitrogenous excretory product
*Formed from excess amino acids
*In liver cells
- Deamination
→Remove amine group and a H atom from amino acid
→Produce ammonia,NH3
→Toxic if allowed to accumulate - Urea cycle(aka ornithine cycle)
NH3 + CO2 →Urea→Excreted (kidneys)
*Keto acid remains→Respired or converted to glucose/glycogen/fat
What are the blood vessels anmd excretory tubes related to the kidney?
Blood vessels:
Renal artery(in)
Renal vein (out)
Excretory tubes:
*Ureter -Urine from kidney into urinary bladder
*Urethra-Urine out from urinary bladder
Describe te structure of the kidney
*Capsule
→Tough, protective layer
*3 main regions:
a)Cortex
b)Medulla
c)Pelvis
*Nephrons-tiny tubes in the kidney in coretx and medulla
Describe the structure of a nephron
1) Bowman’s capsule @ cortex aka renal capsule
2) Proximal convulated tubule @ cortex
3) Loop of Henle @ Medulla
subdivided to:
a)Descending limb
b)Ascending limb
4)Distal convulated tubule @ cortex
5)Collecting duct @ medulla
→Ureter @ pelvis
*Branch of renal artery
→Afferent arteriole
→Glomerulus (tangle of capillaries in the “cup” of the bowman’s capsule)
→Efferent arteriole
→Network of blood capillaries
Surrounding the rest of the nephron
→Branch of renal vein
What are the two stages involved in the mechanism of extraction in the kidneys?
2 stages:
1) Ultrafiltration
*Filtering of small molecules, incl. urea out of the blood @ bowman’s capsule
2)Selective reabsorption
*Absorbing any useful molecules from fluid in nephron
@proximal convulated tubules,loop of Henle, distal convulated tubule and collecting duct
What is ultrafiltration?
*Filtering of small molecules, incl. urea
*Out of the blood in glomerulus
→Into filtrate in bowman’s capsule space/lumen
*Glomerular filtrate is produced
*Flows along the entire nephron
→Into ureter
Describe the structure of glomerular wall and bowman’s capsule wall
Blood in glomerulus is seperated from lumen of bowmans capsule by 3 layers:
1) Endothelium of blood capillaries of the glomerulus
*With many more gaps/fenestrations
2)Basement membrane
*Mesh of collagen and glycoprotein fibres
*Acts as main selective barrier/filter
3)Epithelial cells of bowman’s capsule
*Inner lining of bowman’s capsule (podocytes)
*Wrap around capillaries of the glomerulus
*Podocytes have many finger-like projections that forms gaps/filtration slits
How is the structure of the kidney adapted for ultrafiltration?
1) Many large gaps in capillary endothelium + filtration slits between foot processes of podocytes
*Allow movement of substances from blood plasma easily into bowman’s capsule lumen
2) Diameter of the lumen of afferent arteriole is wider than efferent arterioles
*leads to high blood pressure/hydrostatic pressure in the glomerulus than the bowman’s capsule
*Fluid forced out of glomerulus into bowman’s capsule
3)Basement membrane acts as a filter
→Prevents RBCs,WBCs and large plasma proteins (RMM>68000Da) from passing through
Resulting glomerular filtrate contains:
*No cells and large proteins
*Soluble molecules: water,amino acids, glucose, urea, inorganic ions (Na+,K+,Cl-),uric acid,creatinine,vitamins
→Glomerular filtrate passes through gaps betweens podocytes and into renal capsule
What is selective reabsorption?
*Necessary
*To reabsorb essential substances from filtrate
*Back into blood
*Selective reabsorption so only certain substances are reabsorbed
*E.g. Glucose,amino acids,vitamins,Cl-,Na+,H2O
@proximal convulated tubule, loop of henle. distal convulated tubule and collecting duct
Describe selective reabsorption @ proximal convulated tubule (PCT)
*Main site for glucose/amino acid/vitamin/Cl- reabsorbtion
*Walls made of single layer of cuboidal epithelial cells
1)Active transport of Na+ ions
*From PCT cells into blood in capillary
*VIA Na+/K+ pumps
*Concentration of Na+ ions in the PCT cell decreases
2)Na+ ions in PCT lumen diffuse down its gradient into cells lining the PCT
*By faciliated diffusion
*Via co-transported carrier proteins
*Na+ co-transported with glucose/amino acids/vitamins/Cl- ions into cell
3)Glucose/amino acid/vitamins/Cl- ions diffuse into blood via transport protein
*By faciliatated diffusion
What is the result of selective reabsorption @ proximal convulated tubule (PCT)?
*Glucose is
→ALL actively reabsorbed into blood
→No glucose in urine
*Amino acids,vitamins and Cl- ions
→Actively reabsorbed
*Water, urea
→Some passively reabsorbed
*Uric acid and creatinine → NOT reabsorbed
→Creatinine→Actively secreted/transported into lumen of PCT
What are the adaptations of Proximal convulated tubules cells for selective reabsorption?
a)Numerous microvilli (facing lumen)
-Large surface arwa for absorption
b)Presense of different transport proteins in membranes (facing lumen)
i.e cotransporters,pumps, aquaporins
c)High density of mitochondria
-Provides energy in the form of ATP for active transport
d) High infolding of basal membranes (facing blood capillaries)
e)Tight junctions holding adjacent cells together
-Seperate proteins of front and basal membrane
-So fluid cannot pass between cells,substance must pass through cells
Describe the structure of the loop of Henle
Loop of Henle is located at the medulla
Mainly for water reabsorption
2 parts:
1)Descending limb
*Permeable to both water and Na+ and Cl- ions
2)Ascending limb
*Impermeable to water
*Permeable to Na+ and Cl- ions
How does selective reabsorption occur at the loop of Henle?
@Ascending limb
1. Na+ and Cl- ions move out of the tube
→By active transport
→Into tissue fluid of medulla space
2. High concentrations of Na+ and Cl- ions in the medulla space
→Renal fluid becomes more dilute and enters distal convulated tubule
→Longer loop results in higher concentration of solute built up in the medulla space, more water reabsorption, more conc urine formed!
@Descending limb
*Permeable to both water and Na+ and Cl- ions
Due to high concentrations of solute in the medulla
3. Water moves out into medulla tissue fluid
→By osmosis
→Water is reabsorbed
4. Urea, Na+ and Cl- ions in medulla space diffuse into descending limb
→Fluid in the descending limb becomes very concentrated as it moves down the loop.
Describe how selective reabsorption @ distal convulated tubule occurs.
Distal convulated tubule is located in the cortex
1st part of DCT=Similar to ascending limb of loop of Henle
*Na+ and Cl- ions again actively transported into blood
2nd part of DCT=Similar to collecting duct
*Water is reabsrobed into blood
*Plus secretion of K+,H+ ions and urea into lumen from blood
