PBHM Must know list for urinary system PDF

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These are comprehensive notes for everything you need to know to be successful for the topic of the urinary system within the PBHM course...

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PBHM Must-know list Urinary System (Numbers follow the Chapters in Marieb’s Human Anatomy and Physiology) Excretion: removal of wastes from the body --> urinary system- water, salts and water-soluble wastes Functions of the urinary system: 1. To be the principal means of removal of waste compounds from the body. The medium for this removal is urine 2. The maintenance of the body fluids in a state of HOMEOSTASIS. This is achieved by directly regulating the physical and chemical properties of the blood. For example: – pH – ion concentrations and overall osmolarity – volume/pressure 3. Regulation of the rate of production of red blood cells 4. Vitamin D activation

25.1 Gross anatomy of kidneys • Describe the gross anatomy, three distinct regions of the kidney and its coverings. Regions - renal cortex - renal medulla - renal pelvis

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Trace the blood supply through the kidney.

Coverings - renal fascia: forms a layer that anchors the kidneys in place. - renal capsule: connective tissue layer around the kidney - perirenal/perinephric fat capsule is a layer of adipose tissue between the renal fascia and the fibrous capsule of each kidney. This has a protective “cushioning” function

• Under normal conditions the kidney receives one fifth of cardiac output • The renal artery gives rise to a network of arteries and that in turn branch to form a network of arterioles •The capillary network of the nephron is unusual in that there are two capillary beds: (i) The glomerulus and (ii) a second capillary bed which varies depending which type of nephron that bed is servicing At the nephron •An afferent arteriole gives rise to a multi-looped capillary bed: the glomerulus •The blood drains for the glomerulus into an efferent arteriole •From the efferent arteriole, blood flows through a second capillary bed • From this second capillary bed, blood drains through the venous network of the kidney and ultimately out of the kidney via the renal vein

25.2 Nephrons Describe the anatomy of a nephron (functional unit of the kidney). 1. Bowman’s capsule- folds around and surrounds the glomerulus 2. Proximal tubule (PT) 3. Loop of Henle 4. Distal tubule (DT) 5. The DT of several nephrons drain into in a collecting tubule 6. The collecting tubules from many nephrons will drain in a collecting duct

25.3 How do the kidneys make urine? List and define the three major renal processes: filtration, absorption, secretion. 1. Glomerular filtration- fluid, ions, glucose, and waste products are removed from the glomerular capillaries 2. Tubular reabsorption- selectively moving substances from the filtrate back into the blood. The body keeps what it needs and waste is expelled and/ or becomes urine. 3. Tubular secretion- selectively moving substances from the blood into the filtrate. • Albumin, larger proteins and blood cells largely remain in the blood as it exits the glomerulus • In the tubule the filtrate will undergo processing until what leaves the tubule is essentially urine

25.4 Urine Formation Step 1: Glomerular filtration Be familiar with the forces (pressures) that promote or counteract glomerular filtration. • Exactly how much filtrate enters the capsular space is determined by the balance of: i. The blood pressure inside the glomerulus (the glomerular hydrostatic pressure) that will tend to force plasma out ii. The osmotic pressure brought on by what is dissolved in the blood (the blood colloid osmotic pressure) which will tend to drag fluid into the glomerulus iii. The pressure of any fluid already in the capsular space (capsular hydrostatic pressure) which will oppose more liquid entering from the glomerulus. The result of the interplay between these pressures is the net filtration pressure. Under normal situations this will see a fraction of the plasma forced into Bowman’s capsule.

• Any changes in blood pressure/blood flow, the integrity of the filtration membrane, or capsular hydrostatic pressure will have an impact on glomerular filtration e.g.: 1. Increase in arterial pressure --> increase in glomerular filtration rate (GFR) 2. Dehydration --> decrease in GFR 3. Obstruction to urine flow --> decrease in GFR 4. Glomerular loss --> decrease in GFR

25.5 Urine Formation Step 2: Tubular reabsorption Most of the filtrate is reabsorbed into the blood. • Describe the mechanisms underlying water and solute reabsorption from the renal tubules into the peritubular capillaries.

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Describe how sodium and water reabsorption are regulated in the distal tubule and collecting duct. Sodium reabsorption • If blood pressure drops: this stimulates the secretion of aldosterone from the adrenal cortex • When there are elevated levels of aldosterone in circulation this stimulates further Na+ reabsorption in the distal parts of the tubule --> Water is also re-absorbed through osmosis • This will increase the blood volume (and thus blood pressure) while maintaining the salt content • Aldosterone can also modulate sodium loss and uptake in other parts of the body

Water reabsorption About 180 L of filtrate are produced in the kidneys per day • Urine output is about 1.5 L/day and so.... • Water is reabsorbed by osmosis either via a paracellular pathway or through membranespanning water channels known as aquaporins --> antidiuretic hormone (ADH) controls permeability of water in the aquaporins. • Some 75% of water reabsorption occurs in the proximal parts of the tubule • In distal parts of the tubule additional water reabsorption occurs either: --> coupled with aldosterone- stimulated sodium reabsorption; or --> antidiuretic hormone (ADH)- induced increased expression of aquaporins

25.6 Urine Formation Step 3: Tubular secretion Certain substances are secreted into the filtrate. Describe the importance of tubular secretion and list several substances that are se-creted. Tubular secretion is important for: • Disposing of substances, such as certain drugs and metabolites, that are tightly bound to plasma proteins. Because plasma proteins are generally not filtered, the substances they bind are not filtered and so must be secreted. • Eliminating undesirable substances or end products that have been reabsorbed by passive processes. Urea and uric acid, two nitrogenous wastes, are both handled in this way. • Ridding the body of excess K+. Because virtually all K+ present in the filtrate is reabsorbed in the PCT and ascending nephron loop, nearly all K+ in urine comes from aldosterone-driven active tubular secretion into the late DCT and collecting ducts. • Controlling blood pH. When blood pH drops toward the acidic end of its homeostatic range, the renal tubule cells actively secrete more H+ into the filtrate and retain and generate more HC03- (a base). As a result, blood pH rises and the urine drains off the excess H+. Conversely, when blood pH approaches the alkaline end of its range, CJ- is reabsorbed instead of HC03-, which is allowed to leave the body in urine.

25.7 How do the kidneys regulate urine concentration and volume? • Describe osmotic gradient in simple terms. The osmotic gradient is the difference in concentration between two solutions on either side of a semipermeable membrane, and is used to tell the difference in percentages of the concentration of a specific particle dissolved in a solution.

• Explain how dilute and concentrated urine are formed. 1. When we are over- hydrated, ADH production decreases and the osmolality of urine falls as low as I00 mOsm. If aldosterone (not shown) is present, the DCT and collecting duct cells can remove Na+ and selected other ions from the filtrate, making the urine that enters the renal pelvis even more dilute. The osmolality of urine can plunge as low as 50 mOsm, about one-sixth the concentration of glomerular filtrate or blood plasma.

2. When we are dehydrated, the posterior pituitary releases large amounts of ADH and the solute concentration of urine may rise as high as l200 ,nOsm, the concentration of interstitial fluid in the deepest part of the medulla. With maximal ADH secretion, up to 99% of the water in the filtrate is reabsorbed and returned to the blood, and only half a liter per day of highly concentrated urine is excreted. The ability of our kidneys to produce such concentrated urine is critically tied to our ability to survive for a limited time without water.

25.8 Clinical evaluation of kidney function Describe the normal physical and chemical properties of urine.

25.9 How does the body transport, store, and eliminate urine?

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The ureters, bladder, and urethra transport, store, and eliminate urine. Describe the general location, structure, and function of the ureters, urinary bladder, and urethra. General location

Structure

Function

Ureters

Around the centre of the abdominal cavity.

- Long thin slender tubes

- The urine produced by each kidney drains out through a ureter - Transport urine into bladder

Urinary bladder

Near the pubic region of the abdominopelvic cavity.

The urinary bladder is a smooth, collapsible, muscular sac that stores urine temporarily. - can stretch - can store and stretch without leaking

- Stores urine temporarily that came from the kidneys transported via ureters.

Urethra

Sits right above the genital opening;

The urethra is a thin-walled muscular tube

- Drains urine from the bladder and conveys it out of the body

Compare the course, length, and functions of the male urethra with those of the female. Male Urethra - In males the urethra is relatively long and urine and semen exit the body via the same orifice in the penis

Female Urethra - In the female the urethra is relatively short and empties out into a external urethral orifice anterior to the vagina and anus

This anatomical difference contributes to the greater prevalence of urinary tract infections in females once they become sexually active • Define micturition and describe its neural control.

Micturition- urinating • As the bladder continues to fill, sensory signals also reach the special neurons in the pons which integrates this with information from higher brain centres leading to --> Parasympathetic neurons stimulating the detrussor to contract and relax the internal urethral sphincter • When the time is right=>Cortical signals can inhibit the motor neurons that control the external sphincter causing it to relax • Thus: urination can occur if you are in an appropriate place to do that

Nice to know list (hints will be helpful since info here will be used for the Urinary experiment report) 25.8 Clinical evaluation of kidney function • List several abnormal urine components, and name the condition characterized by the presence of detectable amounts of each. • The rate of glomerular filtrate formation, measured as “clearance”, is an important tool in evaluating renal function. For example quantifying the loss of nephrons in the case of chronic kidney disease • The elevated concentrations of vital low molecular weight chemicals (e.g. sodium) in the urine is an indicator of defective reabsorption • Elevated level of protein in the urine can have a number of causes: defective glomerular filtration; urinary system infections; damage to the renal tubules CLINICAL EVALUATION OF KIDNEY FUNCTION • Because of the ease of collection, urine can be screened for a number of conditions. • This can be conducted through use of urine “strips” made up of a number of indicator squares for particular components of urine: e.g. 1. Glucose (glycosuria): as in diabetes mellitus 2. Ketones (ketonuria): as in starvation or poorly controlled type I diabetes mellitus 3. Bilirubin: a breakdown product of haemoglobin produced in the liver and principally removed inthe faeces . 4. Bilirubinuria can occur in some types of liver and gall bladder disease 5. Haemoglobin (haematuria) bleeding in the urinary system 6. White blood cells (pyuria) infection in the urinary system...