Compendium 7 Notes.docx

Compendium 7 Notes Lecture 1 Gross anatomy of the renal system - 2 kidneys: responsible for the formation of urine - 2 ureters: responsible for the passage of urine - Urinary bladder: responsible for the storage of urine - Urethra: responsible for the passage of urine - Renal capsul...

Compendium 7 Notes Lecture 1 Gross anatomy of the renal system - 2 kidneys: responsible for the formation of urine - 2 ureters: responsible for the passage of urine - Urinary bladder: responsible for the storage of urine - Urethra: responsible for the passage of urine - Renal capsule: connective tissue surrounding each kidney - Adipose tissue: surrounds the outside of the capsule for protection (fat) - Renal fascia: thin layer of connective tissue surrounds the adipose tissue and anchors the kidneys to the abdominal wall Location of the kidneys - Posterior to the parietal peritoneum, on the posterior abdominal wall, lateral to the spine - Note: the right kidney is always slightly inferior to the left - This is because of the position of the liver, it pushes the right kidney down a little - Partially protected by lumbar vertebrae and ribs - 11cm long, 5cm wide and 130g - Note: the adrenal glands are located on top of the kidneys External kidney anatomy - Hilum: small area where the nerves and renal blood supply enters and exits, this is on the medial/ concave side of the kidney - Renal artery: delivers oxygenated blood to the kidney, enters via the hilum - Renal vein: takes away deoxygenated blood from the kidney, exits via the hilum Internal anatomy of the kidney - Hilum: on the concave (medial) side, renal artery and nerves enter, renal vein, ureter, lymphatics exit - The hilum opens into the renal sinus, which is filled with fat and loose connective tissue, the renal sinus is a cavity - Kidneys are organised into two major regions - Outer cortex - Inner medulla (pyramids) - Renal pyramids - Their bases project into the cortex - They are cone shaped - The base is the boundry between the medulla and the cortex - The apex of a renal pyramid is called a renal papilla - Papillae extend into minor calyces (calyx is singular) - The renal pelvis is a single large funnel shaped chamber - The renal pelvis is embedded in the renal sinus, at the hilum it narrows, forming the ureter - Renal columns are extensions of cortical tissue into the medulla (between pyramids) - Papilla -\> minor calyx -\> major calyx -\> renal pelvis The nephron - The functional unit of the kidney - 4 separate nephrons of the nephron, the renal corpuscle, proximal convoluted tubule, loop of Henle, distal convoluted tubule - Blood enters the nephron for filtration - Filtrate/urine is produced - Urine flows: nephron -\> papillary ducts -\> minor calyces -\> major calyces -\> renal pelvis -\> ureter - The loop of Henle is the only part of the nephron which extends into the renal pyramids - The distal convoluted tubule drains into the collecting duct Types of nephrons - There are approximately 1.3 million nephrons in each kidney - Each is approximately 50-55mm in length - Juxtamedullary nephrons: - The renal corpuscle is deep in the cortex near the medulla - A long loop of Henle extending deep into the medulla - 15% of nephrons - Cortical nephrons - Renal corpuscle is located near the periphery/cortex - Shorter loop of Henle - 85% of Nephrons Renal corpuscle - The filtration portion of the nephron - Consists of the glomerulus and the Bowman capsule - Glomerulus: a network/ball of capillaries - Bowmans capsule: enlarges end of the nephron, a double walled chamber, filters the blood/fluid, which then enters the proximal convoluted tubule - Blood enters the glomerulus through the afferent arteriole and filtered blood exits through the efferent arteriole - The afferent arteriold is much larger than the efferent arteriole because the blood is under higher pressure in the efferent arteriole Bowmans capsule - Parietal layer - Outer layer of simple squamous epithelium which then becomes simple cuboidal in the proximal convoluted tubule - Visceral layer - Inner layer, constructed of specialised cells called podocytes, which wrap around the glomerular capillaries to facilitate filtration of the blood The filtration membrane - Fenestrae: the glomerular capillaries are very permeable. Fenestrae are little windows, the innermost layer - Basement membrane: the basement membrane is sandwiched between the endothelial cells of the glomerular capillaries and podocytes - Filtration slits: gaps between the cell processes of the podocytes - Thus, the filtration membrane is specialised for filtration The renal tubules - Proximal convoluted tubule: filtrate drains into here from the Bowman capsule, the proximal convoluted tubule is continuous with the bowmans capsule - Loop of Henle: has a descending and an ascending limb which is continuous with the proximal convoluted tubule - Distal convoluted tubule: shorter than the proximal convoluted tubule - Collecting duct: several distal convoluted tubules connect to a single collecting duct, these have a large diameter. It extends through the medulla and towards the renal papilla towards the ureter Nephron histology - Proximal convoluted tubule: simple cuboidal epithelium with many microvilli. These cells have lots of mitochondria and actively reabsorb Na+, K+ and Cl- ions back into the blood, the convolutions mean that there is a higher surface area for reabsorption - Loop of Henle: the thick parts of the loop are made up of simple cuboidal epithelium and the thin parts are simple squamous for osmosis and diffusion - Distal convoluted tubule: simple cuboidal epithelium with very few microvilli, there are many mitochondria and active reabsorption takes place but not nearly as much as in the proximal convoluted tubule - Collecting duct: simple cuboidal epithelium Major renal veins and arteries - Abdominal aorta: oxygenated blood flowing from the heart to the kidneys - Renal artery (R): branch off of the aorta - Renal artery (L): branch off of the aorta - Renal vein (R): drains into the inferior vena cava - Renal vein (L): drains into the inferior vena cava - Inferior vena cava: deoxygenated blood flows from the kidneys back to the heart - The efferent arteriole branches off into a network of peritubular capillaries around the nephron which eventually drains into the renal vein Urine movement - Pressure forces the urine through the nephron - Smooth muscle forces urine through the ureters - Peristalsis moves urine from the renal pelvis in the kidney to the ureters to the urinary bladder - Ureters enter the bladder obliquely through trigone - Pressure in the bladder compresses the ureter preventing backflow Ureters - Passageway for urine - From renal pelvis to the urinary bladder - Lined with transitional epithelium (can change shape) - Layers of the ureter - Transitional epithelium - Mucosa - Muscularis - Fibrous adventitia - Ureters enter the urinary bladder from the trigone Urinary bladder - The urinary bladder is a hollow muscular container located in the pelvic cavity posterior to the symphysis pubis - The trigone is a histologically unique area on the posterior wall between the entry of the two ureters and the exit of the urethra. This area doesn't stretch to the same extent as other surfaces of the bladder. - The volume of the bladder increases and decreases during the day depending on how much urine is being produced/stored - Layers of the urinary bladder - Transitional epithelium - Lamina proper - Submucosa - Detrusor muscle Urethra - Transports urine from the urinary bladder to outside of the body - Transitional epithelium at the top of the urethra, the rest id stratified columnar - At the junction of the urinary bladder and the urethra is the urinary sphincter - Elastic onnective tissue and smooth muscle prevents urine leakage - External urinary sphincter: skeletal muscle surrounds the urethra as it extends through the pelvic floor - We can voluntarily stop the flow of urine - Male urethra: extends from the inferior part of the urinary bladder to the tip of the penis - Female urethra: shorter and opens into vestibule which is anterior to vaginal opening Lecture 2 Function of the renal system - Excretion: rid the body of waste products. Urine production occurs in the kidneys via filtration of the blood and reabsorption of nutrients. Metabolic wastes and toxic molecules are excreted in urine. - Regulation of blood volume and blood pressure - We control our extracellular fluid levels by producing large amounts of dilute urine or small amounts of concentrated urine - Solute concentration in the blood, extracellular pH, regulation of red blood cell synthesis and regulation of vitamin D synthesis The production of urine - Kidneys: regulate body fluid composition. Sorts chemicals in the blood for removal or for return into the blood - Nephrons: the structural component of the kidney which sorts though all the chemicals and substances in the blood - Urine production: - Filtration -- this occurs as the movement of fluids goes out of the glomerulus, across the filtration membrane and out into the Bowmans capsule, a lot of fluid is being moved, anything small enough will pass through this membrane - Tubular reabsorption -- reabsorption of the good solutes for example water and glucose, back into the interstitial fluid then to the peritubular capillaries so we can use things like water and glucose in other body cells - Tubular secretion -- solutes are secreted across the wall out of the peritubular capillaries through the interstitial fluid and into the nephron filtrate so it can be excteted in urine Process 1: filtration - Movement of fluid derived from blood flowing through the glomerulus and across the filtration membrane - Filtrate: water, small molecules and ions that can pass through the membrane - Doesn't include blood cells, proteins or large molecules - Renal fraction: the proportion of total cardiac output that passes though the kidneys - Varies from about 12-30% in healthy resting humans - Glomerular filtration rate: amount of filtrate produced each minute - 125ml/min or 180L/day - Average urine production per day is 1-2L - Most of the filtrate (99%) must be reabsorbed into the blood - Removes toxins quickly from the blood Filtration membrane - Learn and remember the components of the filtration membrane - Filtrate consists of water, glucose, fructose, amino acids, urea, urate ions, creatine, sodium, potassium, calcium and chlorine - Very little protein is found in filtrate and urine - Filtration is driven by pressure - Blood pressure - Filtration pressure: the force that causes filtration - Pressure gradient responsible for forcing fluid out of the glomerular capillary across the membrane into the lumen of the bowman capsule The juxtaglomerular apparatus - An important regulatory structure located next to the glomerulus - Where the afferent arteriole enters the renal corpuscle, a cuff of smooth muscle cells surrounds it -- the juxtaglomerular cells - A group of specialised cells at a section of the distal convoluted tubule called the macula densa - These secrete an enzyme called renin which is important in the regulation of filtrate formation and blood pressure regulation Process 2: tubular reabsorption - This is the return of water, small molecules (good substances) and ions back into the blood - As filtrate flows through the lumen of the renal tubules - Firstly substances are reabsorbed across the renal tubule into the interstitial fluid, then from here, into the peritubular capillaries then back into circulation - This process takes place in the proximal convoluted tubule, loop of Henle and distal convoluted tubule (under low pressure) - Substances: water, amino acids, glucose, fructose, Na+, K+, Ca+2, Cl-, HCO3 - Proximal convoluted tubule - Majority of reabsorption happens here; the filtrate remaining is about 35% - Active and passive mechanisms of cell membrane transport - Note: the apical surface of the proximal convoluted tubule has simple cuboidal cells lining the nephron and - Boarders with the nephron lumen - Note: the basal surface boarders with the interstitial fluid - Substances in the filtrate that need to be reabsorbed must cross the apical membrane, they are then inside the cell and must cross the basal membrane. Once crossed they are in the interstitial fluid and then back inside the peritubular capillaries - Loop of Henle: some reabsorption of water and ions, remember thick and thin segments - Thin segments -- simple squamous epithelium, highly permeable to water and some solutes can move by diffusion too - The filtrate is further reduced by 15% in the loop of Henle - Ions move through active and passive transport in the loop of Henle - Distal convoluted tubule and collecting duct: some reabsorption - Most of this is under the control of ADH, Anti-Diuretic Hormone - ADH makes the tubule wall more permeable to water and therefore more water reabsorption occurs. This creates less urine, and that urine will be very concentrated - A diuretic such as alcohol or coffee causes the body to increase urine production so an anti-diuretic would do the opposite - Proximal convoluted tubule - Active transport of Na+ across the basal surface -- associated with the reabsorption of most solutes - With Na+ being pumped out of the cell, the concentration of Na+ is low inside the cell. Therefore Na+ moves into the nephron cell through the apical surface. Other substances can move into the cell by symport e.g. glucose - Symport is where a substance 'piggy backs'/harnesses another substance to take it into a cell down the concentration gradient of the second substance - Once the glucose is inside a cell if can diffuse through the basal membrane and then it will end up back in the peritubular capillaries Process 3: Tubular secretion - The movement of non-filtered substances, toxic by-products of metabolism, drugs, or molecules not normally produced by the body, into the nephron for excretion. This occurs mainly in the distal convoluted tubule - Like reabsorption it can be active or passive - Ammonia is a toxic by-product of protein metabolism. It diffuses passively into the lumen of the nephron - H+, K+, and penicillin: actively secreted into the nephron joining the filtrate and becoming urine Urine movement - Pressure forces the urine through the lumen of the nephron - Peristalsis moves urine through ureters to the urinary bladder, every few seconds to every few minutes (fairly constant movement) - Parasympathetic stimulation: increase frequency - Rest and digest - Sympathetic stimulation: decrease frequency - Fight or flight - Prevention of the backflow of urine in the ureters is trigone pressure Composition of urine - 1% of filtrate - 1-2L produced per day - Proportion of water - Depending on the body's needs it varies in concentration - Urea, uric acid, ammonia, creatine, H+, K+ - Bile pigments - Drugs and toxins e.g. penicillin - Urine: - 0.05% ammonia (by product of amino acid break down) - 0.18% sulphate - 0.12% phosphate - 0.6% chloride - 0.1% magnesium - 0.015% calcium - 0.6% potassium - 0.1% sodium - 0.1% creatine - 0.03% uric acid - 2% urea (biproduct of protein break down) - 95% water The micturition reflex - While the flow of urine from the ureters to bladder is continuous, the flow from bladder to urethra is not - The bladder has a capacity of 1L - Micturition is the elimination of urine from the bladder - Full bladder -\> stretch receptors -\> Central Nervous system a message - Voluntary control -\> central nervous system of the external urethral spincter Relax in conjunction with bladder contraction -\> urination Tutorial 2\. the afferent arteriole is larger than the efferent, the glomerulus is the capillary network and the Bowmans capsule is the double layered membrane that surrounds the glomerulus 3\. the two layers of the glomerular capsule are the glomerulus and the Bowmans capsule 4. Fenestrae of capillaries The glomerular capillaries are very permeable, the fenestrae are little windows in the capillaries -------------------------- ---------------------------------------------------------------------------------------------------- Basement membrane The basement membrane is sandwiched between the endothelial tissue and the podocytes Filtration slits Gaps between the cel processes of the podocytes 1. The kidneys lie in the abdominal region of the abdominopelvic cavity 2. Superior to each kidney are the adrenal glands 3. The pelvic cavity 4. The bladder can hold up to... L of urine 1. The liver pushes the left kidney down slightly lower than the right 2. A diagram of the body Description automatically generated 1. The pump is active 2. Up the concentration gradient 3. Na+ out and K+ in 1. Glucose, amino acids 2. Same direction 3. Up the concentration gradient while sodium moves down 4. Sodium potassium pump 1. Calcium 2. Opposite 3. Up 1. Protein embedded in the cell membrane 2. Specific 3. Glucose, amino acids, potassium ions 4. Down 5. Passive 6. Both depending on the concentration gradient 7. Glucose moves from filtrate to blood 1. Water was drawn towards the urea 2. Hypertonic - Dialysis - Dialysis - Blood - Dialysis - Dialysis 2\. Glucose, proteins, lipids, blood (RBC, WBC, platelets) 3\. Sweating via integumentary system, defecation via the digestive system 4\. dialysis is a good substitute temporarily, it is hard to live a normal life when you're stuck at the dialysis center for so long but without it they would die.