Kidney Anatomy & Function

Organs of the Urinary System

Figure 15.1a

Coverings of the Kidneys• Fibrous capsule– Surrounds each kidney, transparent

• Perirenal fat capsule– Surrounds the kidney and cushions against blows

Regions of the Kidney

Figure 15.2b

•Renal cortex—outer region•Renal medulla—inside the cortex•Renal pelvis—inner collecting tube

Kidney Structures• Renal pyramids—triangular

regions of tissue in the medulla

• Renal columns—extensions of cortex-like material inward; separate the pyramids

• Major/minor calyx —tubes that funnel urine towards the renal pelvis

Blood Supply• One-quarter of the total blood supply of the

body passes through the kidneys each minute• Renal artery provides each kidney with arterial

blood supply• Blood leaves the kidneys through the renal

veins

Nephron Anatomy and Physiology• The nephron is the structural and functional

unit of the kidneys• More than 1 million per kidney• Responsible for forming urine• Main structures of each nephron– Glomerulus (knot of capillaries)– Renal tubule

http://www.youtube.com/watch?v=C-Ub0Df44Wk

Nephrons

Figure 15.3a

Nephron Function is Dependent Upon Blood Flow

Nephron Anatomy- Glomerulus AKA Bowman’s Capsule

Figure 15.3c

Nephron Anatomy

Figure 15.3d

Nephron Anatomy• Renal tubule extends from

glomerular capsule and ends at the collecting duct– Glomerular (Bowman’s) capsule– Proximal convoluted tubule

(PCT)– Loop of Henle– Distal convoluted tubule (DCT)

http://www.youtube.com/watch?v=C-Ub0Df44Wk

Nephron Anatomy: Renal Tubule

Figure 15.3b

Nephron Anatomy: Renal Tubule

Figure 15.3b

Urine Formation

1. Glomerular Filtration • Moves: water &

solutes smaller than proteins

• Non-selective& passive

• Fluid = filtrate• Works b/c there’s high

pressure in the capillaries

2. Tubular Reabsorption

• Moves: water, glucose, amino acids, & ions into peritubular capillaries (reabsorbed)

• Depends on body’s needs• Occurs in entire renal tubule – most in proximal convoluted

tubule• Some substances move passively

(water osmosis)• Most move via active transport

(glucose, amino acids)

3. Tubular Secretion • Moves: hydrogen ions,

potassium ion, & creatinine into filtrate from blood into filtrate to be excreted

• Helps get rid of substances not already in filtrate such as drugs or excess potassium

• Helps regulate blood pH

Filtration, Reabsorption, & Secretion in a Kidney

Figure 15.5

Take out a sheet of scrap paper and…

• Define filtration and list 3 things filtered out of the blood

• Define tubular reabsorption and list 3 things that are reabsorbed

• Define tubular secretion and list 2 things that are secreted

Put your name on top and pass it up.

• Kidneys keep these in normal ranges:– Water– pH– Electrolytes

• Kidney allow for the removal of – Nitrogen-containing wastes (urea & uric acid)– Creatinine (from muscle metabolism)

Renal Homeostatic Control

Major Fluid Compartments of the Body

Figure 15.8

Intracellular fluid- in cells

Extracellular fluid- NOT in cells

What is a diuretic?

Hrmmm…

Diuretics…Stuff that makes you pee! Please not in my home.. eew

So then anti-diruetic hormone…• Action: causes water to be reabsorbed

from filtrate• Where: in the DCT & Collecting Duct• How: adds more aquaporins, therefore

more water is reabsorbed• So then why does…

– (alcohol prevents ADH from doing its job, you excrete needed water

Thirst/Water Regulation

pH Balance in Blood & its Regulators

• Buffers are the first line of defense work almost instantaneously

• Secondary defenses take longer to work:– Respiratory mechanisms take several minutes to hours– Renal mechanisms may take several days

Bicarbonate

Aldosterone• What: Hormone that affects Na+

reabsorption

• When released: If blood is diluted & low in volume (from adrenal gland)

• Effect: causes more sodium to be reabsorbed fixes concentration… BUT what about the low volume?

• Where: Works on DCT and collecting duct

Addison’s Disease• Description: Inability to

produce enough aldosterone

• Cause: adrenal glands get attacked by the immune system

• Incidence: 3/100,000 of all ages and sexes

• s/s: chronic fatigue, muscle weakness, loss of appetite, weight loss, low BP, cravings for salty foods

Kidneys help keep Blood Homeostasis by:

1. Maintaining water • Regulates blood volume & BP; uses ADH

2. Regulate pH (~7.4)• HCO3- and H+

3. Keeping electrolytes in balance• Regulates ion/electrolyte levels; uses aldosterone

4. Excretion of nitrogen-containing wastes • Urea- protein amino acids ammonia urea

• Uric acid when nucleic acids are broken down• Creatinine doesn’t have nitrogen but still waste from muscle

metabolism

Contents of Urine• Filtrate vs. urine• Should have: sodium & potassium ions, nitrogen-

containing wastes, ammonia, bicarbonate ions• Should not have: glucose, blood proteins, RBCs,

Hemoglobin, WBCs, bile• Sterile• Colored• pH• Aroma• Density/specific gravity

Abnormal Substances in Urine

Table 15.1

Filtration, Reabsorption, & Secretion in a Kidney

Figure 15.5