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Kidney and homeostasis simplified - Coggle Diagram
Kidney and homeostasis simplified
Homeostasis + Basic knowledge
Deviations from set point are restored by negative feedback
The process of maintaining the body in dynamic equilibrium
where internal state adapts to external environment
Two main functions of the urinary system
Regulation of water and dissolved solutes in plasma
Homeostasis + Osmoregulation
Urea removal from the body via excretion
Important general knowledge
Urine with high concentrations of urea pass through
Ureter > Urinary bladder > Urethra
Deoxygenated blood with lower urea concentration return to the heart through
Renal veins > Vena cava
Oxygenated with higher urea concentration from the heart > kidneys via
The aorta > Renal arteries
Structure of the kidney
Cortex (Outer region)
Has nephrons where ultrafiltration occurs (Glomerular / Bowman's capsule)
Also, selective reabsorption occurs in the PCT
Distinguish structures
Capillaries of glomerulus stained as a dark group
Bowman's capsule, a clear zone surrounding the glomerulus
Cells of PCT are cuboidal with distinct nuclei
Cuboidal cells are square in cross sections
Medulla (Central)
Site of osmoregulation
Controls volume of water and ions lost from blood
Distinguish structures
Thin and thick parts of descending and ascending limb of loop of Henle are different
Collecting ducts appear larger than other structures
Cross sections of varying tubular structures with different diameters and thickness of walls
Blood in capillaries stain as solid mass
Renal Pelvis (Origin)
Distinguish structures
Large number of tubule cut in longitudinal section / along the tubule
Sometimes tubules are visible emptying into a space
This space is the origin of the ureter
Collects urine formed, passing it onto the ureter > bladder
Ultrafiltration
Structure of glomerulus and bowman's capsule
Glomerulus
Surrounded by bowman's capsule
They work together to filter the blood supply going into the glomerulus under high pressure
Pressure must be greater than 6.7Kpa
Blood supply enters through the afferent arteriole and leaves through the efferent
Afferent - Going into
Efferent - Going out
Afferent arteriole is wider, increasing the hydrostatic pressure of blood plasma
Efferent leads to two other capillary networks
"Vasa recta" - Capillaries surround the loop of Henle
Capillaries around the PCT and DCT
Podocytes
Located in the
Bowman's capsules
inner wall
Wraps around the capillaries of the glomerulus
Endothelium
Contains pores between cells to speed up filtration
Pores may be referred to as fenestrations / filtration slits
Pores, allow filtrate to pass from the blood into the lumen of the renal capsule
Protein and cells are too large to pass through
Contains a semi permeable membrane
Basement membrane
In the capillaries and podocytes
Acts as a selectively permeable membrane
The pores are the main filtration site
Smaller than fenestrae and filtration slits
Adaptations
Short diffusion distance between podocytes and capillary
Channels between feet, increases concentration gradient between tissue fluid
The feet increase surface area for filtration
Mechanism
Difference in diameter of the afferent and efferent, increases hydrostatic pressure of blood
Small soluble molecules forced out of plasma
Which enter the channels between podocytes feet and capillary walls
Increased concentrations of these molecules
Basement membrane of the capillary forms a selectively permeable membrane between blood and nephron
Acts as a molecular sieve, allowing small molecules to pass
No cells or plasma proteins
High hydrostatic pressure of plasma from difference of diameters
Osmotic pressure of plasma < filtrate, meaning water moves into plasma
Osmotic pressure is lower from plasma proteins
Fluid pressure in Bowman's capsule increases as volume increases
Total hydrostatic pressure > osmotic pressure of plasma + fluid pressure of filtrate
Called "Net filtration pressure"
Kidney failure and treatment
Causes
Protein
High protein increases urea levels which can be converted to uric acid
This can crystallise and form kidney stones
This can tear and damage tissues
Leads to
Small proteins being excreted by kidneys
Low dietary proteins = accumulation of fluid in tissues, lowering blood pressure and reduction in function
High blood pressure
Leads to excessive filtration by glomeruli and loss of nutrients
Damages glomerulus, if severe, can cause cells and plasma proteins to be lost in urine
Potassium
Required for transmission of nervous impulses and actively transported into cells
High / low concentrations can disrupt nervous transmissions
Can be controlled via diet / drugs
Other
Infections - Treated with antibiotics (bacterial)
Ultrasound breaks down kidney stones - Keyhole surgery removes fragments
Less invasive than open surgery with high recovery rate
Inherited conditions - Incurable, only option is kidney transport
Calcium
Excessive loss leads to reduction of calcium in bones
Causing brittle bone disease (osteoporosis)
Reduced loss, leads to problems with hormonal production, disposition of calcium salt in tissues
Such as the retina (blindness), muscles (contraction pain), joints (movement pain)
Types of kidney failure
Acute
Develops within hours - days
Chance of recovery
Possible causes
Traumatic (e.g. post-surgical)
Acute intoxications
Part of multi-organ failure
Various other diseases (e.g. infections)
Chronic
Develops over years
Irreversible
Possible causes
Secondary to high blood pressure and / or diabetes
Chronic bacterial inflammation of kidneys
Cystic kidneys
Various autoimmune diseases
Treatments
Dialysis
Haemodialysis
Uses a dialysis machine, removing excess water, urea and ions from plasma
Pros
Effective removal of waste products
Care given by trained professional
No equipment to store at home
Cons
Vascular access surgery required
Use of large needles
Schedule inflexibility
Peritoneal dialysis
Uses a selectively permeable membranes in the body to achieve the same result
Pros
No need for needles / vascular access
Schedule flexibility
Cons
Permanent external catheter
Must store equipment at home
Kidney transplant
Living donor
Pros
Shorter waiting time
Less risk of rejection
Last longer (20+ years)
Cons
Pressure on potential donors
Donor only has one kidney
Deceased donor
Cons
Long waiting time
Pain from surgery
Lasts 10 - 15 years
Pros
No dialysis
Healthier
More energy
Selective Reabsorption
Cells and adaptations
Microvilli
Increases surface area for reabsorption
Basal channels
Increases surface area for moving substances into surrounding blood capillaries
Concentration increases in channels, increasing concentration gradient
Mitochondria
Provides ATP for active transport
RER and Golgi bodies
Protein synthesis for facilitated diffusion and active transport
Capillaries in close contact with tubule
Reduced diffusion distance
Constant blood flow, increasing concentration gradient
Mechanism
Water
Osmosis from a higher water potential to lower water potential
From the glomerular filtrate to the cytoplasm of PCT cells
Dilutes cytoplasm until water potential is higher than plasma
Water moves into the tissue fluid > blood
Ions
Sodium is actively transported into the blood capillaries
This reduces the Na+ concentration in the Epithelial PCT cells
Sodium moves from PCT lumen into epithelial cells down the concentration gradient
Sodium is co-transported with glucose or amino acids into the epithelial cells
Co-transport is a mix of facilitated diffusion and active transport
These absorbed molecules diffuse into the capillaries
Hair-pin current multiplier
Reducing water loss
Close proximity of descending and ascending loops maintains concentration gradient
Reabsorbs the remaining water
Ascending limb
As tubular fluid ascends, water potential becomes higher
Or less negative
Sodium + Chloride ions diffuse out of tubule into tissue fluid at the ascending limb's base
Going higher up the tubule, Na + Cl is actively transported out of tissue fluid
Thick ascending tubule
Descending limb
As fluid descends, water potential becomes lower
More negative
Occurs in the medulla
Walls are permeable to water
Therefore, water leaves via osmosis > surrounding tissue > vasa recta
Osmoregulation and Anti-diuretic hormone
Osmoregulation
Maintenance of constant solute concentration and water potential of blood
Utilises negative feedback to bring back optimum values
Osmoregulation system in humans requires the antidiuretic hormone (ADH)
ADH may also be referred to as "vasopressin"
Diuresis is urine production, therefore diuretic reduces urine production
Produced by the
"Hypothalamus"
, a part of the brain
Affects the collecting duct walls and DCT walls
Affecting permeability to water
Decrease
in solute concentration of blood /
increase
in water potential of blood
Causes
Drinking lots of water, less sweating (cold weather), low salt intake / diet
Detector
Osmoreceptors in the hypothalamus
detects
high water potential
of blood, then sends a nervous impulse to the posterior lobe of the pituitary gland
Coordinator
Posterior lobe of the pituitary gland releases
less
ADH into the blood
Effector
Permeability of collecting duct and DCT to water
decreases
Result
Fewer
aquaporins are inserted into the membrane of cells in the collecting duct.
Less
water is reabsorbed from the collecting duct and DCT
Larger
volumes of less concentrated urine produced (Isotonic / hypotonic to general body fluid)
The reverse occurs for the opposite
Aquaporins and ADH
Aquaporins are intrinsic channel-forming proteins
They contain a hydrophilic channel allowing polar water molecules to pass
Connects the lumen of the collecting duct into the tissue fluid
Permanent
aquaporins
Enables constant flow of water into / out of cells
Temporary
aquaporins
Can be inserted or removed from cell membranes
Controls volume of water leaving / entering a cell
Steps
ADH binds to receptors on the membrane
Membrane in contact with the tissue fluid
Releasing membrane-bound vesicles with temporary aquaporins
The temporary aquaporins are attached to the membrane
This fuses with the cell membrane on the luminal side
Luminal side - Cell membrane on the side of the collecting duct cells in contact with the filtrate
Permanent aquaporins allow the entry of water to increase the water potential > tissue fluid
Leads to water moving into the tissue fluid
The water potential in cytoplasm < filtrate, from insertion of aquaporins into the luminal membrane
Leading to water passing in via osmosis
The reverse occurs when ADH level decreases, where aquaporins are recycled into membrane-bound vesicles