Transcript Chapter 14 – Blood

Digestive system
The digestive system break down (digest) feed into a
form that can be absorbed by the body which are the
nutrients (sugars, amino acids and fatty acids), water,
electrolytes and vitamins-organic molecules necessary
for health to the body.
The digestive system organs are separated into two
major groups:
* The alimentary canal or gastrointestinal tract: a
hollow tube extending from the mouth to the anus. It
consists of the mouth, pharynx, esophagus, stomach,
and small and large intestines.
* The accessory digestive organs: include the teeth,
salivary glands, gallbladder, liver, and pancreas.
Histological Organization
of the Digestive Tract
The alimentary canal is a muscular tube made up of 4 layers:
* Mucosa
* Submucosa
* Muscularis externa
* Serosa
HISTOLOGY OF THE ALIMENTARY CANAL
The Mucosa is formed from primarily of epithelium that is invested
with goblet cells. This inner lining of this layer has many tiny folds on
it in order to increase the overall absorptive surface area. This is the
layer of the tract that actually absorbs and secretes (absorbs food,
secretes digestive enzymes).
* The Submucosa in made up primarily of loose connective tissue, blood
vessels, glands, and nerves.
* Muscular
Layer: this layer is made up of 2 layers of smooth
muscle, and provides movement for the tube. The inner layer of
muscle is circular while the outer layer is longitudinal.
* The
Serosa is the outer most layer of the tube and is primarily
composed of serous epithelium and some connective tissue. The
serous layer secretes serous fluid.
Histological Structure of the Digestive Tract
*
Visceral smooth muscle tissue – digestive tract
– a single smooth muscle cell: 5-10um in diameter and 30200um in length
- muscle cells are nonstriated, involuntary muscle
- contractions are as strong as skeletal or cardiac muscle
- muscle cells are arranged in sheets
- 1 cell contracts spreads like a wave throughout the tissue
- contractions lead to 2 types of movement: peristalsis and
segmentation
Contractile filaments of smooth muscle cells are *
not rigidly organized
- plasticity, tolerate extreme stretching, a stretched
cell adapts to its new length and retains ability to
contract on demand
- pacemaker cells in the muscularis mucosae and
muscularis externa undergo spontaneous depolarization
- which trigger contractions leading to 2 types of
movement: peristalsis and segmentation
Peristalsis
* Muscularis externa via
peristalsis propels materials
from 1 region of the tract to
another
* Waves of contractions
move a bolus of food –
1. circular muscles contract
behind the digestive contents
2. followed by longitudinal
muscle contraction that
shorten adjacent segments
3. wave of contraction in
circular muscle layer forces
bolus forward
Segmentation
* Contractions in most areas
of the small intestine and
some regions of the large
intestine churn and fragment
the digestive materials
* The contents are mixed
with intestinal secretions
* No net movement is
produced
THE ALIMENTARY CANAL
* The Mouth is the first item in line in the alimentary canal.
Mechanical
digestion begins here with mastication (chewing).
* The Tongue is an accessory organ of digestion. It functions to position
food in the mouth. It is held to the floor of the mouth by the lingual
frenulum. The top of it is covered with structures called papillae
which help to handle food and provide the sense of taste. The tongue
also helps in the formation of speech.
THE ALIMENTARY CANAL
* The Palate forms the roof of the oral cavity.
It consists of a hard (bony)
anterior portion and a soft posterior portion. A cone shaped projection
called the uvula hangs from the posterior most aspect of the palate.
* The Teeth are the hardest structures in the body. They aid digestion by
way of mastication. There are two sets of teeth in humans, deciduous
and permanent. Children will typically have 20 teeth that are gradually
replaced by the adult teeth. Adults typically have 32 teeth.
THE ALIMENTARY CANAL
The Pharynx is divided into 3 separate regions:
* Nasopharynx
* Oropharynx
* Laryngopharynx
The pharynx is connects the mouth to the
Esophagus. Neither of these organs digest food, but
are important passage ways to the Stomach.
THE ALIMENTARY CANAL
* The
Esophagus
is
a
straight, collapsible tube
that leads from the pharynx
through the thoracic cavity
to the stomach.
It
penetrates the diaphragm
through an opening called
the Esophageal Hiatus.
* The esophagus terminates
at the Cardiac Sphincter
just above the stomach.
THE ALIMENTARY CANAL
The Stomach is a curved pouch-like organ that is located in the
upper left quadrant of the abdomen. The inner lining is marked by
thick folds called rugae.
The stomach secretes Gastric Juice that has a very low pH and
contains an enzyme called Pepsinogen that initiates the digestion
of proteins.
Where most of the organs of digestion have two layers of smooth
muscle to help with peristalsis, the stomach has three layers. This
helps the stomach to churn and mix food in the process of
mechanical digestion.
THE ALIMENTARY CANAL
* The stomach is divided into 4 regions.
- The cardiac region is located lust inside the cardiac sphincter.
- The fundus is the superior most portion located above the
cardiac
sphincter.
- The body makes up the bulk of the organ in the middle.
- The pyloric region is the inferior most area, just above
Sphincter.
The pyloric sphincter retains food in
the stomach until it is released into the
Small Intestines.
the Pyloric
THE ALIMENTARY CANAL
* The
gastric glands contain 3 types of exocrine gland cells that
secrete their products into the lumen of the stomach.
* Mucous neck cells – secrete mucous.
* Parietal cells – produce intrinsic factor.
* Chief
cells – secrete
pepsinogen
and
gastric lipase.
* These
secretions are
called gastric juice
(approximately 2000 –
300 ml per day).