Summary Tissues and Organs

Tissues and Organs
Definitions

 Cells – Basic unit of all living things
 Tissue – are groups of cells that carry out the same function
 Organ – A structural unit made up of several types of tissue grouped to carry out one or more functions
 Organ System – A group of organs working together to carry out a specific function

Both plants and animals have organs

Animals

 Organ Systems in animals are:
o Respiratory system
o Nervous system
o Skeletal system
o Reproductive system
o Digestive system
o Excretory system
o Circulatory system

The Ileum

 The ileum is an organ that is part of the digestive system
 The alimentary canal runs from the mouth to the anus, and it is a long, hollow tube
 The ileum is the final part of the small intestine
 Some digestion will occur in the ileum, but the main role is absorption of the small, simple, soluble products of
digestion into the bloodstream
 The ileum also moves undigested food material to the colon (large intestine)

The ileum is adapted for maximum absorption. Adaptations include:

 Villi and microvilli – these greatly increase the surface area for absorption
 Many mitochondria – in columnar epithelial cells – provide ATP for active transport
 Thin – diffusion distance is smaller
 Good blood supply – capillary network to maintain a concentration gradient

, Mucosa

 The mucosa is the innermost layer of the ileum that is
in contact with the food in the gut lumen
 Most digestive enzymes will be secreted into the
lumen of the ileum, but a lot of digestive enzymes
occur within the cell surface membrane of the
epidermal cells.



Villi

 The internal lining of the ileum is folded into finger-like
projections called villi.
 The villi extend into the gut lumen
 The villi greatly increase the surface area of the
mucosa for the absorption of digested food molecules
 The cells lining the villi are columnar epithelium cells.
 The surface of the columnar epithelial cells has microvilli which further increase the surface area for absorption
 The presence of the microvilli gives the cells a brush border appearance.
 Therefore, the microvilli increase the number of digestive enzymes that would be in contact with food molecules
 The products of digestion are absorbed by facilitated diffusion and active transport – protein carriers are involved
 Each villus has a capillary network and a lacteal
 The villi ‘waft’ in the lumen – this happens because small strands of muscle from the muscularis mucosa extend up
through each villus – when these strands contract, the villi move from side to side


Goblet Cells
 Within the columnar epithelium cells are goblet cells. Goblet cells secrete mucus.
 The mucus provides a slimy, protective layer that lubricates the lining of the alimentary canal – this allows food to
move easily through the ileum (reduces friction).
 The mucus also protects the columnar epithelial cells from the actions of the digestive enzymes – protects the lining
of the gut from the digestive enzymes



Crypts of Lieberkühn

 The Crypts of Lieberkühn are intestinal glands that are embedded in the tissue between the villi. At the bottom of
the crypts, the epithelial cells are continually dividing by mitosis.
 These cells will then move up towards the surface of the villi as the new columnar epithelial cells.
 The cells of the mucosa are continually replaced – they must be replaced as they are constantly worn away due to
friction as the food moves through the gut

Paneth Cells

 Paneth cells are found at the base of the crypts.
 They are responsible for the production of the new epithelial cells and have an anti-microbial function to protect the
actively diving cells that neighbour them at the bottom of the crypt.
 Other cells in the crypt are involved in secreting mucus.