Kidney Function What the nephron does

Objectives Name the parts of the nephron State of functions of the nephron Describe the hormone control of urine Review the urinary system Gain understanding of the Kidney and Nephron from Khan Academy webpage

If I had a million nephrons The nephron is the structure that separates the waste products from the blood Each nephron has its afferent arteriole, glomerulus, efferent arteriole, peritubular capillary bed. The renal artery brings blood into the kidney and branches into these smaller units. The renal vein takes the cleaned blood back into the body.

Four parts four functions Okay, eight letters A is the glomerulus (capillary bed that filters material out of the blood). It is surrounded by the bowman’s capsule, a cup shape end of the nephron. Function 1: filter B is the proximal convoluted tubule where water, most glucose, amino acids and other nutrients and salts are transported back into the blood plasma. Function 2: selective reabsorb C is the distal convoluted tubule where secretion of any excess substances in the blood move into the tubule, such as creatinine, drugs, antibiotics and H+ Function 3: secrete D and E are the collecting duct which leads to the renal pelvis; water can be reabsorbed here too F, G and H form the loop of Henle (descending and ascending) also where water can be reabsorbed Function 4: reabsorption of water and salts

Four parts and four jobs The two kidneys maintain homeostasis of our bodies’ internal fluids Excrete or absorb water to maintain blood volume and osmotic balance as the situation demands: filtered from the glomerulus at the Bowman’s capsule; water reabsorbed in the loop of Henle and collecting duct. Regulate the ion concentration between the extra cellular fluid and the blood through the excretion of inorganic salts (primarily Na+, also K+, Cl-, H+, Ca2+, HCO3 - ): secreted in the distal convoluted tubule Stabilize blood pH so when blood is acidic, H+ is excreted and HCO3 - is reabsorbed AND when if blood is basic, H+ is not excreted and HCO3 - is not reabsorbed: reabsorbed from the proximal convoluted tubule Excrete toxic metabolic by-products such as urea, ammonia, uric acid, and creatinine (a product of muscle activity): urine is transported out through the collecting duct

Four steps of urine formation in the nephron 1. A mixture from the blood is filtered at the glomerulus into the Bowman’s capsule. 2. Water, glucose, amino acids and salts are reabsorbed in the proximal tubule. 3. More water and salts reabsorbed in the loop of Henle and distal tubule. 4. Uric acid, creatinine, hydrogen and ammonia ions and drugs like penicillin are actively transported from the blood into the distal tubule.

Control of urine concentration When you are dehydrated, the kidneys reabsorbs the majority of water from the filtrate which causes urine to be dark yellow. Why? The antidiuretic hormone (ADH) Is made in the hypothalamus, stored and released from posterior pituitary gland Is released in response to low water in the blood (eg dehydration) Controls water reabsorption with a negative feedback cycle. So when you do not drink much water in a given day, the posterior pituitary releases ADH, causing more water to be reabsorbed and less urine to form. Alcohol can upset the water balance because it inhibits the release of ADH which prevents water from being reabsorbed in the nephron and forms more concentrated urine. This leads to dehydration. One of symptoms of a hangover can be solved by drinking water.

Control of urine concentration Two other hormones can influence urine concentration: Aldosterone acts on the collecting duct and causes the body to retain more water. Blood pressure increases when the body retains more water. This system is triggered when there is low blood pressure or low sodium ion concentration in the blood. Aldosterone is part of the renin-angiotensin aldosterone system (RAAS). Arterial Natriurelic Peptide works opposite of the RAAS. This hormone is located in the atrial tissue of the heart. The atrium senses when blood pressure is too high and the heart stretches to release ANP. It acts on the glomerulus of the nephron to increase filtration rate, limits reabsorption of NaCl in the tubules and reduces aldosterone secretion from the adrenal gland

Review Nephron function Urine volume

Urinary system review

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