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Biology 12: Excretion and the Urinary SystemKnowledge

• structures of the urinary system and their inter-relationships• components of the nephron• urine production• kidneys and blood pH• homeostasis of water and sodium levels in the blood

Analyse the functional inter-relationships of the structures of the urinary system

1. Identify and explain the functions of each of the following:– kidney– ureter– urethra– urinary bladder– renal cortex– renal medulla– renal pelvis– nephron

2. Identify and explain the functions of the following components of the nephron:– glomerulus– Bowman’s capsule– afferent and efferent arterioles– peritubular capillary network– proximal and distal convoluted tubules– collecting duct– loop of Henle

3. Describe the production of urine with reference to the following terms:– pressure filtration– selective reabsorption– reabsorption of water following an osmotic gradient– tubular excretion– metabolic waste (e.g., nitrogenous waste, urea, ammonia)

4. describe how the kidneys maintain blood pH 5. compare urea and glucose content of blood in the renal artery with that of the renal

vein6. identify the source glands for antidiuretic hormone (ADH) and aldosterone 7. describe how the hypothalamus, posterior pituitary, ADH, and the nephron achieve

homeostasis of water levels in the blood8. describe how the adrenal cortex, aldosterone, and the nephron achieve homeostasis of

water and sodium levels in the blood

Biology 12: Urinary system

Vocabularyantidiuretic hormone (ADH), adrenal cortex, afferent and efferent arterioles, aldosterone, ammonia, Bowman’s capsule, collecting duct, glomerulus, glucose, homeostasis, hypothalamus, kidney, loop of Henle, metabolic waste, nephron, nitrogenous waste, osmotic gradient, peritubular capillary network, pH, posterior pituitary, pressure filtration, proximal and distal convoluted tubules, reabsorption of water, renal artery, renal cortex, renal medulla, renal pelvis, renal vein, selective reabsorption, tubular excretion, urea, ureter, urethra, urinary bladder, urine

Examine the diagram showing the organs involved in the excretion of waste products of metabolism. Complete the table summarizing the origin of excretory products and the main organs of excretion.


Human Excretion: Introduction

Activity: Structure of the Human Excretory System (25.6) Concepts and connections website

1. On the following diagram of the urinary system, label: inferior vena cava, urinary bladder, ureter, dorsal aorta, kidney, urethra, renal artery, renal vein.

2. List the organs of the urinary system in sequence according to the path taken by urine.

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3. Identify the function(s) of each part of the urinary system:

a. Bladder: _____________________________________________________

b. Ureter: _____________________________________________________

c. Kidney ____________________________________________________

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d. Urethra: _____________________________________________________

e. Renal artery _____________________________________________________

f. Renal vein _____________________________________________________


4. How is the male urethra different from the female urethra in humans? What is the reason for this difference?

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5. What is excretion?

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-The diagram on the right illustrates the products of our body’s breakdown of the food we eat.-Some of these products are very useful (ATP in particular), but others are wastes that we need to deal with.-As we saw in our last unit the respiratory system deals with the CO2 and H2O produced, but now we need to look at another system to see how NH3

(Ammonia) is dealt with.

Protein and Nucleic Acid Digestion-Protein and Nucleic Acids are very important parts of our diet, but they can’t be stored by our bodies. Instead, extra amino acids are turned into carbohydrate and fat storage molecules. However, these molecules don’t use the amino group (NH2), creating nitrogenous wastes.-Animals deal with the NH2 waste product in different ways depending on the environment they live in and their own lifestyles:a) Fish: Aquatic animals can rely on the water in their environment to dilute ammonia, which is very toxic.b) Mammals: Need to convert ammonia into a less toxic form and then excrete it out of the body.c) Reptiles and Birds: Convert ammonia into uric acid, which is less toxic and does not need large quantities of water for excretion.


The liver converts the toxic ammonia into urea, which is less toxic. The urea will travel through the blood stream to the kidneys’ where it will put into urine.*You do not need to know the steps involved in the formation of urea from ammonia! The diagram below is for interest only!


Kidney Structure and Function-Kidneys are made of three components:a) Renal Cortex: Contains the Bowmans Capsuleb) Renal Medulla: Contains the Loops of Henle and Collecting Ductsc) Renal Pelvis: Space lined with smooth muscle where urine collects before being funneled into the ureters.-Within the cortex and the medulla there are nephrons that work to reabsorb useful components of the urea (such as water) back into the blood stream.

BLAST Animation: Kidney Anatomy (25.6)


Identify and explain the functions of the following components of the nephron:

Glomerulus, Bowman’s capsule, afferent and efferent arterioles, peritubular capillary network, proximal and distal convoluted tubules, collecting duct, loop of Henle

-BLAST Animation: How the Kidney Works (25.7)

-Acitivity 25B: Nephron Function

Each kidney contains about 1 million nephrons arranged like this.

Identify the parts of the nephron and the associated blood vessels and give functions for each part:

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Outline the process of urine formation.

-The process of urine formation can be broken down into three steps:

a) Pressure Filtration-Blood pressure causes small molecules (water, salts and nutrient and waste molecules) to leave the glomerulus and enter the Bowman’s Capsule.

b) Tubular Reabsorption-Nephrons have a high surface area because they are so long and twisted. This gives them longer to actively reabsorb nutrient (glucose, amino acids) and salt molecules into the capillary network. It is here that the nephrons can also work to regulate the blood’s pH.-Convoluted tubule cells are also cuboidal and have microvilli, again facilitating reabsorption.-Another advantage of the twisting shape of the nephrons is that substances secreted in one part of the nephron can subsequently help to extract other substances (See the ascending and descending Loops of Henle).

c) Tubular Secretion-The Collecting Duct is permeable to urea in the medulla, contributing to the high salt concentration here that is used to reabsorb water in the descending Loop of Henle.-Some waste materials (excess H+) are also actively transported from the peritubular capillaries into the collecting duct.

d) Excretion-Urine passes into the renal pelvis and then is carried by the ureters to the bladder before leaving the body through the urethra.

*Important Idea: The nephrons return most of the water put into them from the bloodstream. Your kidneys are very improtant in water conservation!

Activity: Control of Water Reabsorption (25.8) and read p.512 to 513


-Use http://www.youtube.com/watch?v=vEXx5YLcGmQ for review too.


https://webmail.ihostexchange.net/owa/redir.aspx?C=cfe4eec3e8d24742b2600c836f0aada3&URL=http%3A%2F%2Fwww.youtube.com%2Fwatch%3Fv%3DvEXx5YLcGmQ

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Here is a more realistic diagram of what a nephron looks like.


Here is a summary of the steps in urine formation:


What causes water to leave the nephron and enter the blood in the loop of Henle and collecting duct?

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C13-4 describe how the kidneys maintain blood pH

How does the kidney maintain homeostasis with respect to pH?

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C13-5 compare urea and glucose content of blood in the renal artery with that of the renal vein

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Hormone Regulation of Kidney Functioning-Your kindeys play a very important role in ensuring that your blood volume remains constant. This can be accomplished in a couple of ways:

a) Reabsorption or excretion of water in the nephrons.-Antidiuretic Hormone (ADH) is produced by the Hypothalamus and released by the Posterior Pituitary Gland when the water content of blood is too low.-ADH triggers the feeling of thirst and makes the collecting duct walls more permeable to H2O so it can be reabsorbed.

b) Reabsorption of Na+ and H2O and arteriole contraction. -The Juxtaglomerular Apparatus (JGA) responds to low blood volume or pressure by releasing the enzyme renin.-Renin breaks down angiotensinogen into Angiotensin I in the blood stream. This is further broken down into Angiotensin II in the lungs. -Angiotensin II causes:i) Constriction of the arteriole leading into the Bowman’s capsule to keep pressure constant for pressure filtration.ii) The adrenal glands to secrete Aldosterone, causing the reabsorption of Na+ and H2O from the distal convoluted tubules.-Blood pressure should increase, inhibiting the producting of renin.


Here is a diagram showing how ADH regulates blood osmolarity via negative feedback:


Here is a diagram that shows how aldosterone regulates blood volume and pressure using negative feedback:

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Complete the concept map.


Fill in information to explain urine formation.


biology 12 - weebly · web viewname: biology 12: excretion and the urinary systemknowledge •...

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