3.7 -homeostasis And The Kidney Flashcards
Define homeostasis
The maintenance of a constant environment
What does the internal environment consist of?
Tissue fluids (that bathe cells supply nutrients and removing waste), maintain glucose confrontation, pH, core temperature and solute potential.
Why do we need to keep the concentration of body fluid at a constant and optimum level?
They protect cells from changes in the external environment, ensuring reactions continue at a constant and appropriate rate allowing cells to function normally despite external changes.
What may alter within the body around a set point? (Dynamic equilibrium)
Body temperature, pH and water potential.
Constant changes occur but a set point is resumed (via homeostasis)
What system controls homeostatic responses?
What do hormones operate by?
The endocrine system.
Negative feedback
Define negative feedback
A change in a system that produces a second change, which reverses the first change.
Give a general die statement about the process Of negative feedback
An output from an effector I.e a muscle or gland, reduced the effect of a stimulus and restores the system to its original level.
Describe the steps of a generalised negative feedback loop
1) the set point for a factor is the norm at which the system operates
2) a receptor detects the level of the factor and its deviation from the set point
3) the receptor sends instructions to a co-ordinator or controller
4) the co-ordinator communicates with one or more effectors i.e muscles and glands, which make responses that are corrective procedures
5) the factor returns to normal monitored by the receptor and information is fed back to the effectors which stop making the correction
Give an example of the negative feedback of glucose
If glucose concentration increases above the set point, insulin is secreted, reducing the glucose concentration by converting it to glycogen and increasing the rate at which it’s respired.
If the level falls below the set point, glucagon is secreted, which results in glycogen being converted to glucose.
Describe the negative feedback of the body’s core temperature
If the body’s core temperature falls below a set point, increased respiration generates heat and construction of superficial blood vessels allows the body to retain it.
If the temperature rises above the set point, superficial blood vessels dilate, and heart radiates from the body, reducing its temperature.
What happens during positive feedback?
An effective increases a change i.e a movement away from the norm cause a further movement away from the norm
Describe how positive feedback is used during pregnancy
Oxytocin stimulates the contraction of the uterus at the end of a pregnancy. The contractions stimulate the production of more oxytocin which increases the stimulus I.e the uterine contractions
Describe the process of positive feedback when you cut your finger
When the skin is cut, the first stage of clot formation is that platelets adhere to the cure surface. They secrete signalling molecules which attract more platelets to the site of the cut.
Define excretion
The removal of metabolic waste made by the body
Describe the metabolic process producing the compounds water and CO2?
In what are the compounds excreted?
What is the excretion organ?
Metabolic process= respiration
Compound excreted in air
Excretory organ= lungs
Describe the metabolic process producing the compound urea.
In what are the compounds excreted?
What is the excretion organ?
Metabolic process= amino acid breakdown
Compound excreted in urine
Excretory organ= kidneys
Describe the metabolic process producing the compound creatinine
In what are the compounds excreted?
What is the excretion organ?
Metabolic process= muscle tissue breakdown
Excreted in urine
Excretory organ= kidneys
Describe the metabolic process producing the compound Uric acid
In what are the compounds excreted?
What is the excretion organ?
Metabolic process= nucleic acid breakdown
Compound excreted in urine
Excretory organ= kidneys
Describe the metabolic process producing the compound bile pigments
In what are the compounds excreted?
What is the excretion organ?
Metabolic process= haemoglobin breakdown
Compound excreted in farces
Excretory organ= liver
How is water removed from the body
Excreted as a metabolic Easter product of respiration
Secreted e.g in tears of saliva
Egested in faeces
What are the two main functions of the kidney
Excretion (the removal of nitrogenous metabolic waste from the body)
Osmoregulation (the control of the water potential of the body’s fluids by regulating the water content)
Define the term osmoregulation
The control of the water potential of the body’s fluids by the regeneration of the water content of the body
Describe protein digestion briefly
Dietary protein is digested into amino acids, which are transported to the liver and then around the body where they are assimilated into protein
What happens to excess amino acids?
They are deaminated in the liver and the amino group is converted to urea
Amino acid—> a-Keto acid + ammonia —> urea
Define the term deamination
The removal of an amino group from a molecule. Excess amino acids are deaminated in the liver, and the amine group is converted to urea.
What happens to other nitrogen containing waste products
They can also be converted to urea, although a low concentration of creatinine is released in both sweat and urine.
Where is urea carried to?
Urea is carried in the plasma to the kidneys and excreted in urine
List the parts of a human kidney
Renal artery (blood into kidney) Renal vein (blood returned to general circulation) Bowmans capsule (ultrafiltration) Cortex Medulla (contains loop of Henle and collecting duct) Nephron Pyramid Pelvis (empties urine into the ureter) Ureter (carries urine into the bladder)
Name the main features that are in the cortex
The glomerulus (containing the bowmans capsule) and the proximal/distal convoluted tubules
What are the main features in the medulla
The loop of henle and the collecting duct
What is the size of the kidney in an adult
Kidney is about:
15cm long
6cm wide
4cm thick
Urter is about:
30cm long
4mm in diameter
What are the main features of the kidney nephron?
Afferent arteriole (blood in) Efferent arteriole (blood out) Glomerulus Bowmans capsule Distal convoluted tubule Proximal convoluted tubule Vasa recta Descending limb Loop of Henle Ascending limb Collecting duct
How many nephrons are there in a human?
There are about a million nephrons in the kidneys, about 30mm long providing a large area for exchange
Where is the bloody carried in the kidneys nephron?
The afferent arteriole (a branch of the renal artery) brings the blood to the nephron, divides into about 50 capillaries in the glomerulus and is from there the filtered blood is carried by an efferent arteriole to the capillary network surrounding the proximal and distal convoluted tubules and the vasa recta.
Define the term ultrafiltration
Filtration under high pressure
Why does the blood arriving in the capillaries of the glomerulus have a high pressure?
1) The hearts contraction Increases the pressure of arterial blood
2) The afferent arteriole has a wider diameter than the efferent arteriole
By what is the blood entering the glomerulus separated from the Bowmans space?
Separated by 3 layers:
1) the wall of the capillary
2) the basement membrane
3) podocytes (the wall of the bowmans capsule)
Describe the structure of the capillary wall
A single layer of endothelium cells with pores called fenestrae, about 80nm in diameter
Describe the structure of the basement membrane
Describe its role
An extra-cellular layer of proteins, mainly collagen and glycoproteins.
It acts as a molecular filter and is the selective barrier, acting like a sieve between the blood and the nephron
Describe the structure of the podocytes (wall of the bowmans capsule)
Made of squamous epithelial cells.
Each podocyte has multiple pedicels wrapped around the capillary pulling it closer to the basement membrane.
The gaps between the pedicels are called filtration slits.
What are the parts of the bowmans capsule
Afferent arteriole Capillaries of the glomerulus Capillary with fenestrae Basement membrane Podocyte Path of filtrate Cells of proximal convoluted tubule
Why is the high blood pressure in the capillaries of the glomerulus essential?
It forces solutes and water through the fenestrae if the capillaries through the basement membrane and through the filtration slits between the pedicels of the podocytes into the cavity of the bowmans capsule.
What does the glomerular filtrate contain
- Water
- Glucose
- Salts
- Urea
- Amino acids
What molecules are too big to be filtered via ultrafiltration and hence remain in the blood
Blood cells
Platelets
Large proteins such as antibodies and albumin.
Describe the water potential in the blood that flows from the glomerulus into the efferent arteriole
It has a low water potential because much water has been lost and there is a high protein concentration remaining.
List the parts of the ultra structure of the wall of glomerular capillary and renal capsule
Fenestrae in capillary endothelium Blood plasma Water potential gradient Hydrostatic pressure gradient Basement membrane Pedicel Filtration slit Podocyte cell of renal capsule wall Bowmans space Path of glomerular filtrate
What is the glomerular filtration rate?
The rate at which fluid passes from the blood in the glomerular capillaries into the bowmans capsule
What determines the glomerular filtration rate?
Determined by the difference in water potential between the two areas (the balance of their hydrostatic pressures and solute potentials).
Define the term selective reabsorption
The uptake if specific molecules and ions from the glomerular filtrate in the nephron back into the bloodstream
What useful molecules does the glomerular filtrate contain?
Glucose
Amino acids
Sodium ion
Chloride ions
What is the proximal convoluted tubule (PCT)?
It is the longest and widest part of the kidney nephron which carries the filtrate away from the bowmans capsule.
What process occurs at the proximal convoluted tubule?
The blood in the capillaries around the PCT reabsorbs all the glucose, amino acids, some of the urea, most of the water and sodium/chloride ions from the filtrate in the PCT.
How is the proximal convoluted tubule adapted from selective reabsorption?
1) large surface area because it is long and there are a million nephrons in the kidney
2) cuboidal epithelium cells in its walls who’s surface area is increased by microvilli
3) cuboidal epithelium cells also have invaginations called basal channels which increase surface area
4) many mitochondria providing ATP for active transport
5) a close association with capillaries
6) tight junctions between the cells of proximal convoluted tubule epithelium prevent molecules o from diffusing between adjacent cells or from the back into the glomerular filtrate