Homeostasis and Excretion: Focus on the Kidney & Nephrons

1. Homeostasis and Excretion: Focus on the Kidney & Nephrons Christen, Deanna, & Stephanie

2. IB Syllabus!

3. Excretory System – The Basics • purpose = dispose of metabolic wastes & control body fluid composition by adjusting rates of solute loss • Three Main Functions [discussed later] • Filtration • Secretion • Selective Re-absorption • Kidney: primary organ involved • Nephron: basic unit of the kidney • Filtrate: liquid from the blood into the nephron • Osmoregulation [water balance] is done through hormones

4. IB Definitions 11.3.1 & 11.3.5 • Excretion: It is the removal from the body of the waste products of metabolic pathways. • Osmoregulation: control of the water balance of the blood, tissue, or cytoplasm of a living organism

5. Capillary 1 Filtration. The excretory tubule collects a filtrate from the blood. Water and solutes are forced by blood pressure across the selectively permeable membranes of a cluster of capillaries and into the excretory tubule. Excretory tubule Filtrate 2 Reabsorption. The transport epithelium reclaims valuable substances from the filtrate and returns them to the body fluids. Secretion. Other substances, such as toxins and excess ions, are extracted from body fluids and added to the contents of the excretory tubule. 3 4 Excretion. The filtrate leaves the system and the body. Urine Basic Excretory Process – See Book for More Detail

6. Kidney • Renal artery/vein – kidney blood flow • Ureter – how urine exits • Urinary bladder – where ureters drain • Urethra– urine elimination tube • Kidney consists of: • Renal cortex – outer region • Renal medulla – inner region • Nephron– functional unit

7. You MUST be able to draw/label this kidney! 11.3.2

8. Nephron • Consists of a single long tubule and a ball of capillaries called the glomerulus. The kidney contains about a million of these. • Strategically placed so the tube winds from cortex (outer), through medulla, then back to cortex, then back down to medulla, and finally to center of kidney: renal pelvis.

9. Be familiar with this nephron!

10. Bowman’s capsule • The nephron tube begins with this bulb-shaped body at one end. A branch of the renal artery (the afferent ateriole) enters into this, branches to form a dense ball of capillaries (glomerulus) and then exits the capsule (efferent arteriole) • Filtration occurs as blood pressure forces fluid from the blood in the glomerulus into the lumen of Bowman’s capsule.

11. Convoluted Tubule • A winding tube that begins with the proximal convoluted tubule at the Bowman’s capsule. • In the middle of the tubule is the loop of Henle which consists of a descending and ascending limb. • Ends with the distal tubule where it joins with the collecting duct. This duct receives processed filtrate from many nephrons which then empties into the renal pelvis, which then drains into the ureter.

12. Selective Reabsorption in the Proximal Convoluted Tubule (11.3.6) • What’s going on: • What: Lots of glomerular filtrate produced: has both waste products and substances that body needs. So… • Response: Body selectivelyreabsorbs these substances into the blood • Where: proximal convoluted tubule • How: microvilli project into the lumen [tiny & lots of em so large surface area]; membrane pumps re-absorb by active transport, using ATP produced by mitochondria (remember osmoregulation?)

13. (continued) • Tidbits to know: • about 80% of mineral ions, including sodium, are taken in • total solute concentration is higher in the cells of the wall than in the filtrate [water then moves from filtrate  cells  adjacent blood capillaries to blood stream]; • 20% of the water’s original volume continues on to the loop of Henle]

14. Cortical and Juxtamedullary • In the human kidney, approximately 80% of the nephrons are cortical meaning having reduced loops of Henle and are in the renal cortex. • The other 20% are juxtamedullary nephrons having well-developed loops extending deeply into the medulla. Only mammals and birds have these nephrons. This enables mammals to make urine that is hyperosmotic to body fluid which is an adaptation essential for water conservation.

15. Review/More Info • afferent arteriole: supplies blood to nephron from renal artery • Bowman’s capsule: surrounds glomerulus • glomerulus: ball of capillaries • efferent arteriole: blood from glomerulus • peritubular capillaries: from efferent arteriole; surround proximal & distal tubules • proximal tubule: secretion & reabsorption • loop of Henle: water & salt balance • distal tubule: secretion & reabsorption • collecting duct: carries filtrate to renal pelvis; permeable to salt • Vasa Recta – capilaries that serve loop of Henle • The Path (as filtrate goes through this pathway urine is made)  • Afferent Arteriole Bowman’s capsule proximal tube the loop of Henle • distal tubule collecting duct renal pelvis ureter 

16. MUST be able to draw/label GLOMERULUS & associated nephron 11.3.3

17. Explanatory Videos! • Kidney/Function of the Nephron • http://www.youtube.com/watch?v=glu0dzK4dbU&feature=related • Kidney/Urination • http://pennhealth.com/encyclopedia/em_DisplayAnimation.aspx?gcid=000136&ptid=17

18. Operations of Nephrons • Three processes: • Filtration • Secretion • Reabsorption

19. Filtration • When blood enters the glomerulus, pressure forces water and solutes through the capillary walls into the Bowman’s capsule. • Solutes like glucose, salts, vitamins, nitrogen wastes, and any other substances small enough to pass through the capillary walls. • Larger substances, such as red blood cells and proteins, remain in the capillaries. • The material that enters the Bowman’s capsule, or filtrate, flows into the convoluted tube.

20. Secretion • As the filtrate passes through the proximal tubule and, later, through the distal tubule, additional material from the intersitial fluids join the filtrate. • This added material, which originates from the capillary network surrounding the nephron, is selectively secreted into the convoluted tubule by both passive and active transport mechanisms.

21. Reabsorption • As the filtrate moves down the loop of Henle it becomes more concentrated due to passive flow of h20 out of the tube. • As it moves up the loop of Henle, it becomes more dilute due to passive and active transport of salts out of the tubule. • At the end of the loop of Henle, the filtrate is not more concentrated but the intersitial fluids surrounding the nephron are more concentrated with salts. • Next, the filtrate descends through the collecting duct toward the renal pelvis. • As it passes through the salts concentrated in the intersitial fluids, water passively moves out of the collecting duct and into the intersitial fluids. • When the filtrate drains into the renal pelvis, it is concentrated urine.

22. Everything put Together! =/ HERE IT COMES….

24. Detailed Diuretic Action in Kidney • It’s a little long, a little monotone, but very detailed and can help answer any remaining questions you may have. • http://www.youtube.com/watch?v=6Wc4f2KnbYo

25. Things for tomorrow… • QUIZ!!!! [study] • Activity before quiz • Powerpoint • Other excretory systems [ie not humans] • Hormones involved • Osmoregulation in the kidney • Forms of nitrogenous wastes