GI 3: Secretion

GI Secretion

the production and release of fluids/substances into the lumen of the GI tract

- by mucosal cells and/or accessory GI organs

- Overall functions of secretory glands in GI Digestive enzymes

- Mucus for lubrication and protection

Gastrointestinal Secretion Volumes

>7 L of fluid is secreted into the GI tract each day

- not including approximately 2 L of daily fluid intake in the diet

Fluid secreted into the GI tract is mainly composed of?

Water, Mucus & Ions

- important Hormones & Enzymes also contribute functionally to GI secretions

Secretions along the GI tract are highly Variable in Composition, depending on?

1. Mucosal Cell Type within the segment

- APUD, Parietal, Chief, Goblet, etc.

2. Accessory Organs

- Salivary Gland, Pancreas, Liver

Gastrointestinal Secretion Composition

• Water

• Mucus

• Ions

• Enzymes

• Hormones

types of GI secretory glands

1. Goblet cells

2. Brunner's Glands

3. Tubular Glands

4. Crypts of Lieberkuhn

5. APUD cells

6. Accessory glands

Goblet cells

− Single-celled glands lining the GI mucosa

− Found everywhere in GI, but abundance is largest in the colon

Goblet cells Function

secrete mucus

- onto the mucosa

- lubricates and protects surface from abrasion and chemical digestion

Brunner's Glands

− Compounds glands

- located near the proximal duodenum

Brunner's Glands Function

secrete alkaline mucus

- neutralizes gastric acid → protects the mucosa

Tubular Glands

Location: stomach and duodenum

cells:

- parietal cells

- chief cells

Tubular Glands Function

protein digestion and GI immunity

1. parietal cells: acid secreting

- Digestion + Immunity

2. chief cells: pepsinogen secreting

- Protein Digestion

Crypts of Lieberkuhn

− Deep pits/invaginations formed by mucosal folds

- mainly in small intestine

− Contain villi for absorption

- Contains several types of secretory cells, including Goblet cells and enterocytes

Crypts of Lieberkuhn Function

Goblet cells and enterocytes secrete:

- digestive enzymes

- H2O

- ions

- Mucus

facilitate lubrication, digestion and absorption

APUD cells

− Single-cell mucosal endocrine glands

- mainly small intestine

APUD cells Function

Secrete various GI hormones

- endocrine regulation of GI functions

Accessory glands

- Salivary Glands

- Pancreas

- Liver

Salivary Gland Function

Secretes saliva

- Lubrication/Protection

Pancreas Function

Secretes Enzymes + HCO3-

- Digestion and Acid Neutralization

Liver Function

secretes bile

- Fat Digest./Absorption

Apud (enteroendocrine) cells are best described as:

A. Exocrine glands releasing mucus

B. Endocrine cells secreting GI hormones into the bloodstream

C. Neurons releasing VIP and GRP

D. Hepatic cells detoxifying blood

B. Endocrine cells secreting GI hormones into the bloodstream

Which of the following glands primarily secretes digestive enzymes and bicarbonate?

A. Salivary glands

B. Pancreas

C. Brunner's glands

D. Crypts of Lieberkühn

B. Pancreas

Basic mechanism of stimulation of secretion

1. Contact of food

A. Direct stimulation of glandular epithelium

B. Activation of enteric nervous system

2. Autonomic stimulation

A. Parasympathetic

3. Hormonal regulation