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

SPECIALISED CELLS & STRUCTURAL HIERARCHY [CSEC BIOLOGY & HSB]

-
Image
SYLLABUS REFERENCE  HSB [A4] identify selected cells which make up the human body;  [A5] explain the importance of cell specialisation in humans;  CSEC BIOLOGY  [B1.5] explain the importance of cell specialisation in multicellular organisms;  SPECIALISED VS UNSPECIALISED CELLS  Unicellular organisms are just one cell in size. These cells are said to be unspecialised or undifferentiated . In unicellular organisms, these cells are independent, carrying out all the life processes by themselves.  Multicellular organisms consist of up to trillions of cells, depending on the organism. In a multicellular organism, there are great differences between cells, even as they have the same basic structure. Each type of cell is specialised to do a specific job, such as feeding, support, communication, or defense.  A specialised cell is a cell that has been changed to carry out a specific job in a multicellular organism. Differentiation / Cell Specialisation is the Process of Becoming Specialised  S
Read more

BIOLOGICAL OBSERVATION [CSEC BIOLOGY]

-
Image
SYLLABUS REFERENCE  [A1.1] group living organisms found in a named habitat based on observed similarities and differences.  Lesson Outcomes  By the end of this lesson, you will be able to: observe living organisms, following the principles of biological observation; describe living organisms and their structures, using appropriate scientific language;  compare organisms, according to the structures observed and described. 
Read more