FOOD INGESTION AND MASTICATION REFLEX

LEARNING OBJECTIVE

• At the end of lecture student must be able to know,• The digestive system and body system,• Ingestion,• Saliva secretion,• Mastication defination,function,control.

THE DIGESTIVE SYSTEM AND BODY METABOLISM

• Digestion– Breakdown of ingested food

• Absorption– Passage of nutrients into the blood

• Metabolism– Production of cellular energy (ATP)

ORGANS OF THE DIGESTIVE SYSTEM

• Two main groups

– Alimentary canal – continuous coiled hollow tube

– Accessory digestive organs

ORGANS OF THE ALIMENTARY CANAL

• Mouth• Pharynx• Esophagus• Stomach• Small intestine• Large intestine• Anus

PROCESSES OF THE MOUTH

• Mastication (chewing) of food• Mixing masticated food with saliva• Initiation of swallowing by the tongue• Allowing for the sense of taste

INGESTION

• Ingestion is the consumption of a substance by an organism.

INGESTION

• The amount of food that a person ingests is determined principally by intrinsicdesire for food called hunger.

• The type of food that a person preferentially seeksis determined by appetite.

MASTICATION

•

Processes involved in food preparation, including moving unchewed food onto the grinding surface of the teeth, chewing, it, and mixing it with saliva in preparation for swallowing

FUNCTIONS

1. To lubricate the bolus with salivary secretion

2. To breakdown the bolus to small particles3. To begin digestion of carbohydrate (amylase)

SALIVARY SECRETON

Anatomy • Parotid glands • Submandibular (submaxillary) glands• Sublingual glands• Smaller glands in mucosa of tongue, palate, etc.

COMPOSITION OF SALIVA

Aqueous fluids Water, ions and enzymesParotid, submaxillary and sublingual glands

Mucus secretion (mucin) Submaxillary and sublingual glands

AQUEOUS FLUIDS

H2O, K, HCO3, Na, Cl, a-amylase, lingual lipase, IgA, kallikrein, muramidase (lyses muramic acid of Staphylococcus), lactoferrin and EGF

Hypotonic Solution Ions Na, K, CI, HCO3: (concentrations altered with altered flow rates) At low flow rate High K and HCO3 Low Na and CI−

ENZYMES

a-amylase, parotid glands • cleaves a -1 ,4-glycosidic bonds • pH optimum of 7 • inactivated @ pH 4 but continues to work for sometime in

unmixed food in orad portion of stomach Lingual lipase

• hydrolyzes lipids • continues working into duodenum

Kallikrein (protease, acinar cells)• Catalyzes production of bradykinin from a-globulin• Increase local blood flow

Water (0.5 L saliva/day)

CHARACTERISTICS OF SALIVA AND FLOW RATE

• Daily secretion = 800-1500 mL

• PH = 6-7

FUNCTIONS OF SALIVA

• moistens food• begins digestion • adjusts salt appetite • Contains factory that destroy bacteria

Thiocyanate ions and antibodies lactoferrin which chelates iron necessary for bacterial growth Lysozyme:

i. active against bacterial wallsii. Helps thiocyanate in entering bacterial wall and where they

become bactericidal

CONTROL OF SECRETION

• Unique aspects of control of salivary secretion secretion rate depends entirely on neural control -ANS both Parasympathetic and Sympathetic lead to increase secretion Composition modified by Aldosterone

increases Na, Cl reabsoption increases K secretion

PARASYMPATHETIC Origin

salivary nucleus in medulla Outflow

CN VII & IX Transmitter

Ach Increased stimulation in response to

conditioned reflexes (taste, smell) Decreased stimulation due to

sleep, fear, dehydration Stimulates

- initiation & maintenance of secretion (protein poor, high k and HCO3)

- contraction of myoepithelial cell - metabolic rate - blood flow - direct innervation of blood vessels

- growth Sectioning of parasympathetic markedly decreases flow & leads to

atrophy

SYMPATHETIC

Origin- intermediolateral gray T1-T3

Transmitter- norepinephrine

Stimulates - secretion (mostly enzymes)

- contraction of myoepithelial cell- metabolic rate

Stimulates (cont)- growth

Sectioning of sympathetic nerves has minimal impact on secretion

STIMULATION OF SALIVA SECRETION

MASTICATION OR CHEWING

The first step in the breakdown of complex foodstuffs and serves several functions, including:

• Breaking large pieces into small pieces, resulting in a massive increase in surface area, which is where digestive enzymes work.

• Softening of food and transformation into a size conducive to swallowing

• Lubrication of food by impregnating it with saliva

TEETH ORGANIZATION• Anterior teeth (incisors) for cutting

• Posterior teeth (molars) for grinding

• All the jaw muscles working together can close the teeth with a force as greatas 55 pounds on the incisors and 200 pounds on the molars

• The presence of a bolus of food in the mouth at first initiatesreflex inhibition of the muscles of mastication, which allows the lower jawto drop.

• The drop in turn initiates a stretch reflex of the jaw muscles that leadsto rebound contraction.

• This automatically raises the jaw to cause closure of theteeth.

• It also compresses the bolus again against the linings of the mouth,which inhibits the jaw muscles once again, allowing the jaw to drop and rebound another time.

• This is repeated again and again.

MUSCLES OF MASTICATION

• Mastication is accomplished through the activity of the four muscles of mastication

MUSCLES OF MASTICATION

• The masseter.• The temporalis (the sphenomandibularis is considered a part of the

temporalis by some sources, and a distinct muscle by others)• The medial pterygoid.• The lateral pterygoid.

MUSCLES OF MASTICATION

• The mandible is the only bone that moves during mastication and other activities, such as talking.

• While these four muscles are the primary participants in mastication, other muscles are usually if not always helping the process, such as those of the tongue and the cheeks

INNERVATION

• Most of the muscles of chewing are innervated by the motor branch of thefifth cranial nerve, and the chewing process is controlled by nuclei in the brainstem.

• Stimulation of specific reticular areas in the brain stem taste centers willcause rhythmical chewing movements.

• Also, stimulation of areas in the hypothalamus,amygdala, and even the cerebral cortex near the sensory areas fortaste and smell can often cause chewing.

REFERENCES

• Guyton.• Internet(different sources)