Identify the structures labelled A to G in the diagram above, and describe their function in terms of the excrertory system

*Refer to the diagram on page 328 in your text

Label      Structure           Function

A           Renal Artery      carries blood from the 

                                    aorta into the kidney

                                    for filtration 

B           Renal Vein        carries filtered blood 

                                    from the kidney to the

                                    inferior vena cava

C           Aorta                brings oxygen-rich

                                    blood from left side

                                    of heart to organs of

                                    lower body, including

                                    the kidneys via the

                                    renal arteries

D           Kidney              filters blood; reabsorbs

                                    nutrients, waters and

                                    other useful molecules;

                                    removes metabolic

                                    waste products; helps

                                    regulate blood volume;

                                    helps maintain pH of

                                    blood

E            Ureter              carries urine from

                                    kidney to the urniary

                                    bladder

F            Urinary             temporarily stores

              Bladder            urine

G           Urethra             carries urine to the

                                    external environment

Antidiuretic hormone (ADH) plays a role in water abosorption.  When ADH is present, more water is reabsorbed (blood volume and pressure rise), and a decreased amount of urine results.

AOne example of ADH release occurs on a warm day.  The hypothalamus will be stimulated to release ADH if an individual does not drink much water to be reabsorbed and less urine is formed.

If blood pH is too acidic, H+ ions are actively transported from the blood into the urine.  This process takes place in the distal tubule. 

The kidneys also help regulate the levels of bicarbonate ions in the blood.  Bicarbonate ions pass freely through the capillary walls in the glomerus and enter the glomerular filtrate.  The concentration of bicarbonate in the glomerule 

fluid is equivilant to that of plasma.  If bicarbonate ions are not reabsorbed, the buffering capacity of the blood will be rapidly depleted.  The process of reabsorption of the bicarbonate ions primarily occurs in the proximal tubule, although some can be reabsorbed from the distal tubule.

The following is a partial list.

• Blood leaving the kidney has a much lower concentration of urea (nitrogenous waste)
• Blood leaving the kidney has a much lower concentration of uric acid (nitrogenous waste)
• Blood leaving the kidney las a lower concentration of potassium ions (under hormonal control).
• Blood leaving the kidney will have a lower concentration of metabolites (drugs, products of metabolic reactions in the body) (tubular secretion).
• Blood leaving the kidney has the same concentration of glucose( glucose actively reabsorbed)
• Blood leaving the kidney has the same concentration of amino acids (amino acids actively reabsorbed).
• Blood leaving the kdiney has less ammonia (tubular excretion).

Four types of dissolved substances found in the filtrate include nitrogenous wastes (urea, uric, acid), glucose, amino acids, and salts

(Na+, Cl-, HCO3-)

The flow chart is one way to show the kidneys control water levels in this situation.

blood plasma dilute---> osmoreceptors signal to stop releasing ADH ---> distal tublule and collecting duct less permeable to water ---> more water excreted in the urine

Filtration occurs when whole blood enters the glomerus.  Due to blood pressure in the glomerulus, water and small molecules move from the glomerulus to the inside of the glomerular capsule.  This is a filtration process because large molecules and formed elements in the blood are unable to pass through the capillary wall.  Tubular Reabsorption occurs as molecules and ions are both passively and actively reabsorbed from the neprhon into the blood of the capillary network that surrounds the nephron.  When sodium ions are actively reabsorbed, chloride ions follow passively.  The reabsorption of salt (NaCl) increases the concentration of folutes in the blood, and water will move from the tubule into the blood by osmosis.

Tubular secretion of salt along the thick portion of the axcending limb produces an osmotic gradient.  Because of the osmotic gradient within the renal medulla, water leaves the collecting duct and moves into the capillary bed surrounding the nephron.

Osmosis  is the diffusion of water across a semi-permeable membrane.  Tubular secretion and reabsorption establishes osmotic gradients in the kidney, which, in turn, regulates the balance of water in the body.

How would each of the following processes in the kidney change in response to serious dehydration in the body caused by excessive sweating on a hot day?

a) glomerular filtration

b) tubular reabsorption

c) ADH secretion

(a)     Glomerular filtration would be less (dehydration would reduce blood pressure).  Angiotension released by the adrenal glands is a vasconstrictor that increases blood pressure.

(b)     Tubular reabsorption would create increased levels of ADH, resulting in increased reabsorption of water in the collecting duct.  Aldosterone stimulates the distal tubule and collecting ducts to reabsorb sodium ions, which allows more water to reabsorb.

(c)     ADH secretion would increase the permeability of the distal tubule and collecting duct, resulting in more water being removed from the urine (increased concentration of urine).

(a) Identify the structures labelled A to E on  this diagram.

(b) Describe the primary functions of each of the following sections of the human kidney.

i) cortex                               iii) collecting duct

ii) medulla                            iv) renal pelvis

*Refer to the diagram on page 328 in your text

The functions of sections of the human kidney are as follows

(i) Cortex: the processes of filtration (lomerulus).  Tubular reabsorption (proximal tubule) of materials required by the body are removed from the filtrate and returned to the bloodstream.  Tubular secretion (distal tubule) involves the active transport of material out of the blood and into the distal tubule.

(ii) Medulla: cells of the medulla have an increased concentration of Na+ ions.  The high levels of Na+ are the result of active trasport of sodium ions out of the ascending limb of the nephron.  Reabsorption of water (osmosis) occurs in the collecting ducts as they pass through this region.

(iii) Collecting duct: reabsorption of water by osmosis as urine moves through.  Collecting ducts pass through renal medulla.

(iv) Renal pelvis: a central space that is continuous with ureter.  The collecting ducts deliver urine to the renal pelvis.

a) Identify each of the structures labelled A to K.

b) Describe the functions of the following structures

i) glomerulus

ii) Bowman's capsule

iii) proximal tubule

iv) descending loop of Henle

v) ascending loop of Henle

vi) distal tubule

vii) collecting duct

* Refer to the diagram on page 328 in your text

The following chart identifies the structures in the diagram shown.

Label                        Structures

A                          Bowman's capsule

B                          renal artery

C                          renal vein

D                          loop of the nephron

E                          capillary network

F                          proximal tubule

G                          glomerulus

H                          distal tubule

I                           renal cortex

J                           renal medulla

K                          collecting duct

i) glomerulus: glomerular blood pressure forces some of the water and dissolved substances from the blood plasma through the pores of the glmerular walls

ii) Bowman's capsule:  receives filtrate from the glomerulus

iii) proximal tubule:

Reabsorption:

• active reabsorption of all nutrients, including glucose and amino acids
• active reabsorption of positively cahrged ions such as sodium, potassium, calcium
• passice reabsorption of water by osmosis
• passive reabsorption of negatively charged ions such as chloride and bicarbonate by electrical attraction to positively charged ions 

Secretion

• active secretion of hydrogen ions

iv) Descending of loop of Henle:

 Reabsorption:

• passive reasorption of water by osmosis

v) Ascending loop of Henle

 Reabsorption:

• Active reabsoprtion of sodium ions
• Passive reabsorption of chloride and potassium ions

vi) Distal tubule

 Reabsoprtion

• Active reabsorption of sodium ions
• Passive reabsorption of negatively charged ions such as chloride and bicarbonate
• Passive reabsorption of water by osmosis

Tubular Secretion

• Active secretion of hydrogen ions
• Passive secretion of potassium ions by electrical attraction to chloride ions

vii) Collecting duct

 Reabsorption

• Passive reabsorption of water by osmosis