BIOL Chapter 17 Digestive System

What are the general functions of the digestive system?

the mechanical and chemical breakdowns of food

mechanical - breaks down large pieces of food into smaller ones, but does not change chemical composition

chemical - uses enzymes to break down food particles, by changing them into simpler chemicals

What are other functions of the digestive system?

ingestion

propulsion

secretion

digestion

absorption

elimination

Which organs constitute the digestive system?

Mouth

Esaphogus

Stomach

Small intestine

Large intestine

Rectum

Anus

2 divisions of the digestive system

alimentary canal - food passageway, muscular tube, abt 8m long, mouth pharynx, esophagus, stomach, small intestine, large intestine, and anal canal

accessory organs - organs that empty secretions into alimentary canal, salivary glands, liver, gallbladder, pancreas

Describe the wall of the alimentary canal.

composed of 4 layers

mucosa - deepest layer

submucosa

muscularis

serosa - superficial layer

Mucosa

directly surrounds the lumen (the passageway)

innermost layer

mucous membrane

absorbs dietary nutrients

secretes mucus and enzymes

Submucosa

connective tissue layer

contains blood and lymphatic vessels, nerves, glands

nourishes cells

transports absorbed food molecules

Muscularis

muscle tissue

contains circular and longitudinal layers

moves tube and food materials

Parasympathetic impulses

(rest and digest)

increase activities of digestive system

Sympathetic impulses

(fight or flight)

inhibit digestive actions

What are 2 types of movement in the alimentary canal?

mixing movements - muscle in small sections contracts rhythmically, does not move materials in one direction, churning in stomach (segmentation)

propelling movements - moves materials in one direction, propels food particles down the tract in wavelike motion (peristalsis)

What are the functions of the mouth?

ingestion

secretion

mastication - chewing and mechanical digestion

chemical digestion

propulsion

What are the purposes of the cheeks?

keeps food inside the mouth

stratified squamous epithelium

Purpose of lips?

sensory receptors

judge temp and texture of food

orbicularis oris muscle

What is the purpose of the tongue?

to move food

Which is harder, bones or teeth?

teeth are stronger than bones

they are not bones

hardest structure in the body

How do primary teeth differ from secondary teeth?

20 primary (deciduous, baby) teeth; replaced by secondary teeth

32 secondary (permanent, adult) teeth

What are incisors for? What are canines for? What are molars for?

incisors used for biting

canines for grasping and tearing

molars and premolars for grinding

Where does chemical digestion start?

in the mouth with saliva

What are the functions of saliva?

dissolves food so it can be tasted

moistens food particles and binds them together

contains enzymes - begins chemical digestion of carbs

bicarbonate ions - keep pH favorable for enzyme activity and protect teeth from acidic foods

What stimulates the salivary glands to secrete saliva?

Salivary secretions

serous cells - produces watery fluid, amylase splits starch and glycogen into disaccharides

mucous cells - secretes mucus

What are the functions of the esophagus?

muscular tube

propulsion and secretion

What are the functions of the pharynx?

secretion and propulsion

Swallowing mechanisms: 3 stages

First stage: voluntary stage, saliva is mixed with chewed food, forming a bolus

Second stage: food reaches oropharynx, triggers swallowing reflex, muscles contract to send food down

Third stage: food enters esophagus, peristalsis transports food in esophagus to stomach

What are the functions of the stomach?

receives food from esophagus

secretes gastric juices

chemical digestion - initiates protein digestion

churning (segmentation) - motility, mixes food with gastric juice

absorption - has limited absorption

motility - peristalsis moves food into small intestine

Gastric secretions

gastric glands are in gastric pits

contains 4 types of secretory cells - mucous neck cells, chief cells, parietal cells, and enteroendocrine cells

What keeps the stomach from digesting itself?

the mucous - provides lubrication and protects stomach lining

Gastric secretions: gastric juice

pepsinogen - secreted by chief cells, inactive form of pepsin

pepsin - active enzyme that breaks down proteins into polypeptides

gastric lipase - fat-splitting enzyme, found in small quantities, action inhibited by acid

hydrochloric acid - converts pepsinogen into pepsin; produced by parietal cells

intrinsic factor -

chemical messengers -