EXCRETION | KIDNEY STRUCTURE & FUNCTION [CSEC HSB & BIOLOGY]

-

SYLLABUS REFERENCE 

CSEC HSB

  • [B1.27] distinguish between egestion and excretion; 
  • [B5.1] explain the importance of excretion in human beings; 
  • [B5.2] explain the roles of the organs involved in excretion; 
  • [B5.3] relate the structures of the kidney to their function; 
  • [B5.8] explain the regulation of water; 

CSEC Biology 

  • [B5.1] distinguish between egestion and excretion; 
  • [B5.2] discuss the importance of excretion in living organisms; 
  • [B5.3] state how metabolic wastes are excreted from plants and animals; 
  • [B5.4] relate the kidney to its osmoregulatory and excretory functions. 

EXCRETION VS EGESTION 


Excretion is the removal of metabolic waste products. 
Metabolic waste products are products of biochemical reactions that occur in cells of the organism. 

Egestion is the removal of undigested food out of the digestive system. 
These substances would have never participated in biochemical reactions in the organism's cells. 

WHY IS EXCRETION IMPORTANT? 


Metabolic waste products are dangerous to the organism! 

They can interfere with the other biochemical reactions in the body in various ways. Therefore, if they are allowed to accumulate, they can poison the organism and cause harm, even to the point of being lethal. 

PATHS OF EXCRETION IN PLANTS AND ANIMALS 

In Plants 

Plants generally excrete by depositing the waste products into parts of the plant, that are later shed. 
Examples include leaves and bark. 

In Humans & Large Animals 

There are several pathways:
  • Sweating, which removes small amounts of urea and salts.
  • Breathing, which removes carbon dioxide. 
  • Release of urine, a product of the urinary / excretory system. This is the most important pathway. 

THE URINARY SYTEM IN DETAIL




GROSS STRUCTURE OF THE KIDNEY 







NEPHRON 










HOW DOES THE KIDNEY PRODUCE URINE?




Ultrafiltration 

  • Filtration of blood under pressure.
  • Afferent arteriole supplies the glomerulus, which then empties into efferent arteriole. 
  • Afferent has a large diameter (wider) than efferent arteriole. This greatly increases pressure into glomerulus. 
  • Increased pressure forces blood against porous capillary walls, and molecules below a certain size passes through, into the Bowman's capsule. 


Selective Reabsorption & Secretion 

  • Besides the waste, such as urea, the filtrate also contains useful substances. This must be returned to the blood to ensure survival. 
  • All the glucose is reabsorbed. A percentage of salts and other substances are also reabsorbed. 
  • Selective reabsorption happens via active transport, at the proximal and distal convoluted tubules. 
  • Extra toxins are secreted into the tubules from the surrounding capillaries (aka peritubular capillaries). 

Water Absorption 

  • Water is moved from the Loop of Henle to the surrounding capillaries via osmosis. 
  • The loop dips into the medulla region. This area has a high salt concentration. The resulting concentration gradient encourages the flow of water out of the loop, into the surrounding capillaries. 

Osmoregulation

  • Water is removed from filtrate according to the body's needs, under the control of the anti-diuretic hormone (ADH). 
  • If the body is dehydrated, ADH is released. 
  • Its presence increases the permeability of walls of the distal convoluted tubule & collecting ducts. As a result, more water is reabsorbed into the bloodstream, which leads to a reduced volume of concentrated urine. 
  • The opposite happens if the body is very hydrated. 


Urine Collection

  • The solution leaving the collecting duct is now called urine. 
  • The collecting ducts merge into each other and the urine empties into the kidney pelvis. 
  • The urine is then transferred to the bladder via the ureter. 





 

Popular posts from this blog

HUMAN REPRODUCTION [CSEC HSB & BIOLOGY]

-
Image
SYLLABUS REFERENCE  CSEC BIOLOGY  [B9.2] describe the structure & function of the reproductive systems in humans;  [B9.3] describe the menstrual cycle;  [B9.4] outline the mechanism for bringing gametes together, their fusion, and the development of the embryo in humans;  CSEC HSB [B7.2] describe the structure and function of the reproductive systems in human beings;  [B7.3] describe the menstrual cycle;  [B7.4] explain ovulation, fertilisation, implantation, and development of the embryo;  [B7.5] describe the stages of the birth process; 
Read more

RESPIRATION, GASEOUS EXCHANGE, AND BREATHING [CSEC BIOLOGY & HSB]

-
Image
SYLLABUS REFERENCE  CSEC HSB  [B2.1] explain the importance of breathing in humans;  [B2.2] relate the structures of the respiratory tract to their functions;  [B2.3] describe the breathing mechanism;  [B2.6] distinguish between gaseous exchange and breathing;  [B2.7] identify characteristics common to gaseous exchange surfaces;  [B2.8] differentiate between aerobic and anaerobic respiration;  CSEC BIOLOGY  [B3.1] describe the process of aerobic respiration; [B3.2] distinguish between aerobic and anaerobic respiration;  [B3.3] describe the mechanism of breathing in humans and gaseous exchange in flowering plants;  [B3.4] identify characteristics common to gaseous exchange surfaces; 
Read more

NERVOUS vs ENDOCRINE SYSTEM [CSEC HSB & Biology]

-
Image
SYLLABUS REFERENCE  CSEC HSB [B6.1] describe the main divisions of the nervous system;  [B6.2] distinguish between a neuron and a nerve;  [B6.3] explain the functions of motor and sensory neurons and spinal synapses;  [B6.4] describe the functions of the parts of the brain;  [B6.5] describe the mechanisms of a reflex action;  [B6.6] explain the process by which voluntary actions occur;  [B6.7] distinguish between a voluntary and involuntary action;  [B6.8] explain the response of the sense organs to stimuli;  [B6.13] compare and contrast endocrine and nervous control systems;   [B6.14] identify the sites of hormone production;   [B6.15] explain the roles of selected hormones in the human body;  CSEC Biology  [B7.1] define 'stimulus' and 'response';  [B7.2] describe the response of: (a) green plants to stimuli; (b) invertebrates to variations in light intensity, temperature and moisture;  [B7.3] define r...
Read more