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Human Biology > Week 10 Digestive system > Flashcards

Week 10 Digestive system Flashcards

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1
Q

Digestive processes within the body (6)

A 
- Ingestion
• Propulsion
• Mechanical breakdown
• Digestion (enzymatic)
• Absorption
• Defecation
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2
Q

The 2 main parts of the digestive system

A 
The gastrointestinal
tract/ alimentary canal
• Tube which food travels
through from mouth to
anus
 The accessory organs
• Helps with digestion but
is not part of the tract
and food does not pass
through them.
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3
Q

Where does digestion occur?

A 
- Mouth: Salivary amylase:
Carbohydrates
• Stomach: Pepsin:
Proteins
• Small intestine: Bile and
pancreatic juice: Lipids
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4
Q

Two groups of the digestive system organs:

A

-Organs of the
Gastrointestinal (GI) tract

• Accessory digestive
organs

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5
Q

What is peristalsis

A
  • Propels food along GIT
  • Involuntary
  • Unidirectional
  • Note: Adjacent segments
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6
Q

What is segmentation

A
  • Mixes content in the small intestines
  • Nonadjacent segments
  • Increases absorption
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7
Q

Digestion

  • Ca________
  • Pr_________
  • Li_______
A

Involves Digestive Enzymes
Carbohydrases (eg. disaccharidases)
• breakdown complex carbohydrates/disaccharides
• example - salivary amylase in saliva in mouth

Proteases
• breakdown proteins to peptides  amino acids
• example - pepsin in the stomach

Lipases
• breakdown fats to fatty acids + monoglycerides
• example - pancreatic lipases in pancreatic secretions

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8
Q

Absorption

A 
Small Intestine
• Carbohydrates
• Amino acids
• Lipids
• Nucleic Acids

Large Intestine
• Vitamins/minerals
• Electrolytes
• Water

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9
Q

Absorption

A 
Small Intestine
• Carbohydrates
• Amino acids
• Lipids
• Nucleic Acids

Large Intestine
• Vitamins/minerals
• Electrolytes
• Water

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10
Q

Defecation (poo)

A

Excretion mechanism for solid waste
• Expels indigestible substances
• Example - cellulose

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11
Q

Major layers of the GIT

A 
The Mucosa of the GIT
• innermost layer of GI tract
• secretes mucus, digestive
enzymes and hormones
• absorbs nutrients
• protects against infection via
MALT (mucosa-associated
lymphoid tissue)
• possesses its own thin layer of
smooth muscle cells
– muscularis mucosae
– twitch constantly to dislodge
adhering material
– folds into the villi of small intestine
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12
Q

Mucosal Epithelium

A 
Stratified squamous
epithelium:
• mouth, oesophagus and anus
(for protection against wear and tear)
Simple columnar
epithelium:
• everywhere else
(for nutrient absorption)
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13
Q

Mouth Anatomy & Digestive Processes

A

Mouth (buccal (oral) cavity)
• Continuous with the oropharynx
• Tongue
• Interlacing bundles of skeletal muscle fibres.
• Mixes food with saliva.
• Forming a bolus by pushing food against the
hard palate.
• Initiates swallowing by pushing bolus into
pharynx.
• Teeth
• Enamel, dentin and cement all calcified but
avascular
• Enamel lacks collagen
• Salivary glands

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14
Q

Salivary Glands (3)

A

Three major sets of salivary glands in the mouth

  • Sublingual Gland
  • Parotid gland
  • Submandibular gland
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15
Q

Composition of saliva

A 
Salivary Glands Secrete 1.5L/24h
•Largely water
•Slightly acidic
•Electrolytes (Na+, K+ Cl-
, PO43
- and HCO3-)
•Proteins: mucin, lysozyme, IgA
•Metabolic wastes (urea and uric acid
  • Moistens food to aid in swallowing
  • Cleanses the mouth
  • Prevents overgrowth and infection of harmful bacteria
  • Dissolves food particles so they can be tasted – Contains salivary amylase – breaks down amylose (starch)
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16
Q

GIT Structures: The Pharynx and Oesophagus

A 
Oropharynx and below:
• below nasopharynx
• contains tonsils and epiglottis
Oesophagus:
• muscular tube (25cm)
•Through mediastinum of the thorax
• passes through the diaphragm
• joins stomach at the
gastro-oesophageal sphincter
17
Q

Lesser and Greater Omentum

A

Two mesenteries tether the stomach to other digestive organs
and cavity wall.
• Greater Omentum also contains a lot of fat deposits
• Appearance of a lacy apron.
• Contains lymph nodes

18
Q

Emptying the stomach

A

Food mixed with gastric juice becomes Chyme.
• Pyloric part holds 30ml of chyme
• During peristalsis about 3ml of chyme moves into
the duodenum of the small intestine via the Pyloric
valve,
• The rest is propelled backward and remixed.

19
Q

Digestive Processes of the Liver

A
  1. Produces bile (500-1000mls per day)
    • pH 7.6 to 8.6 (alkaline)
    • yellow-green in color
    • Main bile pigment is bilirubin (yellowish)
    • Waste product of heme from worn-out RBC’s
    • Metabolised by bacteria in small intestine to Stercobilin
    (brown) which gives it’s colour to faeces.
    • Bile emulsifies fats → aids fat digestion/absorption
    • Bile salts keep cholesterol dissolved within bile
  2. Metabolises lipids and other nutrients
  3. Generates large amounts of ATP
  4. Detoxifies toxins, alcohol, drugs, waste products
  5. Primary site for glucose storage for the body
    • in the form of glycogen
    All liver functions are assisted by the:
    Enterohepatic (portal) circulatory
    system
    • delivers blood directly from the small
    intestine to the liver
    • Recycles bile salts!
20
Q

The Gallbladder

A

Small green sac lined with smooth muscle
• Right, lower surface of liver
• Stores and concentrates bile before release into
small intestine
• Gallbladder contraction is stimulated by intestinal
hormone – cholecystokinin
• Cholecystokinin is a hormone released when acidic, fatty
chyme enters small intestine from the stomach

21
Q

The Pancreas

A 
Endocrine Gland:
• Islets of Langerhans
•Insulin, Glucagon,
Somatostatin, Grehlin
•Exocrine Gland:
•Acini: Clusters of
Acinar cells.
•Produces digestive
enzymes (1.2L per day)
22
Q

Exocrine Region of the Pancreas

A 
Zymogen granules
• Contains proenzymes
(inactive enzymes)
• Ducts
• Transport secretions
• Duct cell secrete
bicarbonate and
water (pH8)
23
Q

Region of the small intestine (3)

A 
Main site for nutrient absorption
Three regions -
• duodenum (first 25cm)
• jejunum (2.5 metres)
• ileum (last 3.6 metres)
24
Q

Structure anatomy of small intestines

A 
Structural modifications
for absorption
• Circular folds
• Slow the passage of food
• Villi
• The core of which has a
dense capillary bed and a
wide lymphatic capillary
• Microvilli
• Cytoplasmic extensions
• Fuzzy appearance
(brush border)
• Plasma membranes
contain enzymes
25
Q

Cell types of the Small Intestine

A 
Enterocytes
• Simple columnar cells
• Absorb nutrients and electrolytes
• In crypts, secretory cells • Intestinal juice
• Goblet cells
• Secrete mucus
• Enteroendocrine cells
• Secrete hormones to regulate gastric
secretion.
• Intestinal crypts only
• Paneth cells
• Deep in the crypts
• Produce defensins and lysozyme
• Stem cells
• Produce all the cell types
26
Q

Gross Anatomy of the Large Intestine, 4 main sections

A 
1. The caecum
• pouched sac
• contents of small
intestine enter here
• contains appendix
(circled)
2. The colon
• ascending
• transverse
• descending
• sigmoid
(sigmoid = S-shaped)
  1. The rectum
    (rect = straight)
  2. The anal canal
27
Q

Features of the large intestine

A 
Reclaims remaining
water and electrolytes:
• Teniae coli (ribbons)
• Longitudinal muscle
layer is reduced to three
bands
• Haustra (to draw up)
• Tone of the teniae coli
causes pocket-like sacs
• Epiploic appendages
• Small fat-filled pouches
(significance unknown)
28
Q

Microscopy of the large intestine

A 
• No circular folds, villi or
brush border
• Simple columnar
epithelium
• Thicker mucosa
• Tremendous numbers of
goblet cells
29
Q

Bacterial Microbiota of the Large Intestine

A 
Home of thousands of
different types of bacteria
• Recover energy from
otherwise indigestible foods
• Downside 500ml of gas/day
• Synthesise some vitamins
• B complex vitamins and Vit K
• Beneficial bacteria outcompete/suppress
harmful bacteria
• Evidence indicates bacterial species in
gut influence weight, health and mood!
30
Q

The end of the line:

Rectum and Anal Canal

A 
Rectum (= straight)
• Walls stretch when
containing faeces:
• Defecation reflex.
• Rectal valves
• Anal canal
• Internal anal sphincter
• Involuntary
• External anal sphincter
• Voluntary
• Hemorrhoidal veins

Human Biology (10 decks)

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