Excretory sysytem Flashcards
What are the functions of the Kidneys/ Excretory system?
Excretion: removal of organic waste products from bodily fluids.
Elimination: of these waste products into the environment
Homeostatic: regulation of the volume and solute concentration of blood plasma.
Regulating blood volume and pressure by adjusting the volume of water loss in the urine, releasing erythropoietin and releasing renin.
Regulating plasma concentration of sodium, potassium, chloride and other ion, by controlling the quantities lost in the urine and controlling calcium ion levels throughout synthesis of calcitriol.
Help stabilising blood pH through controlling loss of hydrogen and bicarbonate ions in the urine.
Conservation of valuable nutrients by preventing their excretion in urine while excreting organic waste products- especially nitrogenous waste such as urea and uric acid.
Assisting the liver in detoxifying poison and during starvation, deminating amino acids so that other tissues can break them down.
All of these process occur so that the blood composition is kept within acceptable limits. Disruption to any one of these will have immediate and potentially fatal consequences.
Describe the key anatomical structures of the kidney
The kidneys are located either side of the vertebral column at position T12/L3 the right kidney lies slightly superior to the left kidney. The superior surface of the kidneys is capped with adrenal glands. The kidneys are found between the muscles of the dorsal body wall and the parietal peritoneum, in a retroperitoneal position.
The position of the kidneys is maintained by the overlying peritoneum, contact with adjacent visceral organs and supporting connective tissues.
The following 3 connective tissues support and protect the kidneys:
The renal capsule: a layer of collagen fibers that surrounds the entire outer surface of the organ.
The adipose capsule: a thick layer of adipose tissue that covers the renal capsule.
The renal fascia: a dense fibrous outer layer that extends outwards from the renal capsule through the adipose capsule to this layer. It anchors the kidney to the surrounding structures. Posteriorly the renal fascia fuses with the deep fascia surrounding the muscles of the body wall. Anteriorly the fascia forms a thick layer that fuses with the peritoneum.
All of the above protect the kidneys from shock and jalts in everyday life. If the collagen fibers are broken or disrupted it can result in a floating kidney which is particularly dangerous as it leaves the ureter and renal vessels susceptible to twisting and stress.
Each kidney is around 10cm long, 5.5cm wide and 3cm in thickness. 150g each.
The renal sinuses and cavities are lined with the renal capsule, which stabilises their position. The renal sinuses are also filled with renal adipose tissue. The hilus is the point at which the renal artery and nerves, lymphatics, enter and ureter vein, lymphatics,exit the kidneys.
The kidney has two layers the outer cortex and the inner medulla. The cortex is a superficial portion of the kidney in contact with the renal capsule. The cortex is reddish brown and granular. The medulla consists of 6-18 renal pyramids that have base that faces the cortex and an apex known as the renal papilla that projects into the renal sinus. The renal pyramids have multiple fine grooves that converge at the renal papilla.
Cortical tissue runs between each renal pyramid called renal columns, which have a granular texture similar to the cortex. Renal lobes of the kidney refers to each of the renal pyramids the overlying cortex and half of the adjacent renal columns either side of the renal pyramid. The striated appearance of the pyramids is caused by microtubules.
The urine is produced in the renal lobes. Renal ducts found in papilla discharge urine into cup shaped minor calyx to major calyx to renal pelvis to ureter to bladder to urethra to conduct the urine to the external environment.
Describe the blood supply and innervation of the kidneys
20-25% of our total cardiac output is received by the kidney. That’s around 1200ml of blood every minute. They receive blood from the renal artery that originates from the abdominal aorta.
The flow of blood through the kidneys is as follows:
Renal artery, segmental arteries, interlobar arteries, arcuate arteries, interlobular arteries, afferent arterioles, (Nephron: glomerulus, efferent areterioles, peritubular capillaries), venules, interlobular veins, arcuate veins, interlobar veins, renal vein.
Describe the structure of the nephron
Nephrons are known as the basic functional unit of the kidney. Nephrons are microscopic tubular structures found in the cortex of each renal lobe. Each kidney has roughly 1.25 million nephrons. The length of the nephron can be 50mm.
The nephron begins at the renal corpuscle a spherical structure consisting of Bowman’s capsule and a capillary network known as the glomerulus. The glomerulus projects in to the Bowman’s capsule. The renal corpuscle is the site where the process of filtration occurs.
The renal tubule has two convoluted segments the CT proximal convoluted tubule and the DCT distal convoluted tubule; separated by the U-shaped loop of Henle. The convoluted segments are in the cortex and the loops extend partly or completely into the medulla .
The filtrate produced is called the tubular fluid when travelling in the tubules. Collecting ducts receive the fluid from the many nephrons starting in the cortex and descending to the medulla , carrying fluid to the papillary ducts that drains into the caylx and then the renal pelvis and so on.
Around 85% of nephrons are cortical nephrons. Here the loop of Henle is relatively short.
The remaining 15% of nephrons are called juxtamedullary nephrons. They have long loops of Henle that descend deep into the medulla. in these nephrons the peritubular capillaries are connected to the vasa recta a long straight capillary that lies parallel to the loop of Henle. The tick and thin of the loop of Henle refers to the height of epithelium not the diameter of the lumen. Cubodial epithelium are found in the thick and sqauamous epithelial in the thin. (passive water reabsorption occurs here).
PCT has a larger diameter than the DCT and the PCT has microvilli where the DCT does not.
JGA secretes a hormone called erythropoietin and the enzyme renin. The JGA consists of the juxtaglomerular cells and associated macula densa. It is specifically the juxtaglomerular cells that secrete the renin.
3 main functions: Glomerular filtration (filtrated based on size), tubular reabsorption, tubular secretion (blood pH regulation).
Quiz to do to go over my knowledge
https://highered.mheducation.com/sites/0070272468/student_view0/chapter20/feedback_multiple_choice_quiz.html
Discuss nervous control of the kidneys
The kidney and ureters are innervated by renal nerves. Most of the nerve fibers involved are sympathetic postganglionic fibers from the celiac pleuxus and the inferior splanchnic nerves. A renal nerve enters each kidney at the hilus and follows the tributaries of the renal arteries to reach individual nephrons. The sympathetic innervation adjusts rate or urine formation by changing blood flow and blood pressure at the nephron and stimulates the release of renin which restricts loss of water and salt in the urine by stimulating reabsorption at the nephron.
Discuss the three main organic waste products.
Urea: Produced during the breakdown of amino acids. Most abundant type of organic waste. 21g produced each day.
Creatinine: produced by skeletal muscle tissues by the breakdown of creatine phosphate, a high-energy compound that plays an important role in muscle contraction.
Uric acid: is formed from the recycling of nitrogenous bases from RNA molecules. Approx. 480mg of uric acid a day.
Discuss the GFR and its control.
Around 1.5-2L of urine are produced a day.
Protein is not found in the GF.
The average GRF is 180L per day.
Blood pressure creates a sufficiently high hydrostatic pressure within the glomeruli to overcome the osmotic forces in the blood. Most proteins are too large to pass through the tight capillary pores in the glomerulus.
There are high amounts of Na in the urine and low amounts of uric acid. Although glucose is lost through filtration, all of it is reabsorbed into the blood in persons without supervening disease.
How is systemic blood pressure regulated by the kidney?
In the walls of the afferent arterioles there are specialised smooth muscle cells. This allows detection of the blood pressure. When blood drops then these cells respond by releasing a enzyme called renin, vice versa at high blood pressures. The specific area/ cells that secrete renin are the juxtaglomerular cells in the JGA.
The liver produces the protein angiotensinongen. This circulates in the blood and becomes active when acted on by renin. The renin clips a small peptide from angiotensinogen to produce angiotensin 1. So the lower the blood pressure the more renin that acts upon angiotensinogen and the more angiotensin 1 produced.
How is systemic blood pressure regulated by the kidney?
In the walls of the afferent arterioles there are specialised smooth muscle cells. This allows detection of the blood pressure. When blood pressure drops then these cells respond by releasing a enzyme called renin, vice versa at high blood pressures.
The liver produces the protein angiotensinongen. This circulates in the blood and becomes active when acted on by renin. The renin clips a small peptide from angiotensinogen to produce angiotensin I. So the lower the blood pressure the more renin that acts upon angiotensinogen and the more angiotensin I produced.
Another enzyme ACE present in the lungs converts angiotensin I to angiotensin II by making it smaller.
Angiotensin II stimulates :Vasoconstriction peripheral arterioles, increasing peripheral resistance which increases blood pressure.
Also stimulates the secretion of aldosterone from the adrenal cortex which increases the reabsorption of Na from the DCT renal tubules into the blood which results increase osmotic pressure leading to water volume increase, intravascular voulme increases venus return to the heart so that increases CO, leading to increase blood pressure.
Angiotensin II also effect GFR
Describe the cell types throughout the nephron
PCT: The cubodial microvilli form a brush border on the epithelial cells in the proximal tubule that effectively increase its surface area for permeability. Thin loop of henle has simple epitheila, thick ascending and DCT have cubodial without microvilli, collect duct has columnar.
The ureters have smooth muscle which causes peristaltic waves to move the urine.
The bladder lining is made of transitional epithelium.
The lining of the bladder can be distended without tearing the protective coating of the mucous layer.
What is the renal threshold mechanism?
Sodium does not have a renal threshold mechanism, glucose, creatine, ascorbic acid and citric acid do.
How much sodium is actively reabsorbed by the proximal segment of the nephron?
About 70% of the sodium that will be reabsorbed will occur at the proximal tubule.
Which blood vessel conveys blood out of the nephron?
Blood is not considered to be completely out of the nephron until it enters a vein. And so it leaves via the interlobular vein.
Ureter, Bladder, Urethra, urination.
Peristalsis makes the urine flow from the kidney to the bladder.
The bladder and smooth muscle tubes are all under autonomic involuntary reflex control; the only muscle which can be controlled by desires is the external urethral sphincter.
The micturition or urination reflex involves a reflex arc entering the sacral portions of the spinal cord.
The detrusor muscle is the strong muscle of the urinary bladder.
