unit 15

Digestion

Mechanical and chemical breakdown of foods and absorption of nutrients

Mechanical digestion

Breaks down large nutrient molecules into smaller chemicals, by breaking down chemical bonds

Chemical digestion

breaks down large nutrient moleclues into smaller chemicals, by breaking chemical bonds

Mucus

secreted in small intestine by goblet cells, which are abundant throughout the mucosa, and the mucus-secreting glands located in submucosa of the duodenum

Submucosa

(Apart of the wall Alimentary canal). Lies under mucosa, consist of loose connective tissue, housing blood and lymphatic vessels, nerves, and glands. Nourishes the surrounding layers of canal, vessels transport absorbed nutrients away from digestive organs

Muscalaris

(Apart of the wall Alimentary canal) Consist of 2 layers of smooth muscle: inner circular layer and outer longitudinal layer. Propels food thru canal

Serosa

Apart of the wall Alimentary canal, outer serous layer, or visceral peritoneum. Protects underlying tissues, and secretes serous fluid to reduce friction between organs

Mucosa

Apart of the wall of Alimentary canal. The inner layer of the wall, a mucus membrane that surrounds the lumen of the tube. Consist of epithelium, underlying connective tissue, and a smooth muscle. Protects tissues of canal and carries secretion and absorption of dietary nutrients

Alimentary canal

Muscular tube that passes through thoracic and abdominopelvic cavities, food passageway between the mouth and anus. \~8 meters long

Segmentation

in the small intestine aids mixing by alternately contracting and relaxing the smooth muscle in each area

Mixing movements

Occur when smooth muscles contract rhythmically in small sections of the tube

peristalsis

Propelling movements Include a wavelike motion called

Propelling movements of the tube

A ring of contraction in a portion of tube occurs, while relaxation occurs of the ring, allowing a mass of food to be propelled to the next segment of the tube

The mouth

The first portion of the alimentary canal. Function: receives food, and begins mechanical digestion by **mastication** (chewing). surrounded by lips, chees, tongue, and palate

Vestibule

The narrow space between the teeth, cheeks, and lips is called

Vitamins

•Organic compounds required in small amounts for normal metabolic processes (other than carbohydrates, lipids, and proteins)

•Not produced by cells in adequate amounts, so considered essential nutrients

Two classifications of vitamins

•**Fat-soluble** (A, D, E, and K)

•**Water-soluble** (B vitamins and C)

Fat soluble vitamins

Vitamin A,D,E and K

What are fat soluble vitamins

Dissolved in fats, and are influenced by the same factors that influence liquid absorption, stored in moderate quantities in the body which can lead to overdose.

Vitamin A

Exists in several forms; \n synthesized from carotenes; stored in liver; stable in heat, acids and bases; unstable in light

Function:

An antioxidant necessary for synthesis of visual pigment, mucoproteins, and mucopolysaccharides; for normal development of bones and teeth; and for maintenance of epithelial cells

Vitamin D

A group of steroids; resistant to head, oxidation, acids, and bases; stored in liver, skin, brain, spleen, and bones

Function:

Promotes absorption of calcium and phosphorus; promotes development of teeth and bones

Vitamin E

A group of compounds; resistant to head and visible light; unstable in the presence of oxygen and ultraviolet light; stored in muscles and adipose tissue

Function:

An antioxidant; it prevents oxidation of vitamin A and polyunsaturated fatty acids; may help maintain the stability of cell membranes

Vitamin K

Exists in several forms ; resistant to head, but destroyed by acids, bases, and light; stored in liver

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Function:

Required for synthesis of prothrombin, which functions in blood clotting

Water soluble vitamins

Vitamin B and Vitamin C

vitamin B

Are necessary for normal cellular metabolism in the oxidation of carbohydrates, lipids, and proteins

Vitamin C

(ascorbic acid) is needed for the production of collagen, the metabolism of certain amino acids, iron absorption, and synthesis of some cholesterol-based hormones

Thiamine (vitamin B1)

Destroyed by heat and oxygen, especially in alkaline environment

Function:

Part of coenzyme required for oxidation of carbohydrates; coenzyme required for ribose synthesis

Riboflavin (vitamin B2)

Stable to heat, acids, and oxidation; destroyed by bases and ultraviolet light

Function:

Part of enzymes and coenzymes required for oxidation of glucose and fatty acids and for cellular growth

Niacin (nicotinic acid) (vitamin B3)

Stable to heat, acids and bases; converted to niacinamide by cells; synthesized from tryptophan

Function:

Part of coenzymes required for oxidation of glucose and synthesis of proteins, fats, and nucleic acids

Biotin (vitamin B7)

Stabel to heat, acids, and light; destroyed by oxidation and bases

Function:

Coenzyme required for metabolism of amino acids and fatty acids, and for nucleic acid synthesis

Folacin (folic acid) (vitamin B9)

Stored in liver

Function: Coenzyme required for metabolism of certain amino acids and for DNA synthesis; promotes production of normal red blood cells

Dietary Minerals

in elements, derived from the soil, which are essential to human metabolism

Characteristic of minerals

•Responsible for 4% of body weight

•Concentrated in the bones and teeth

•May be incorporated into organic molecules or inorganic compounds, while others are free ions

Minerals

Comprise parts of the structural materials in all body cells, may be portions of enzymes, contribute to the osmotic pressure of body fluids, and play roles in conduction of nerve impulses, muscle contraction, coagulation of blood, and maintenance of pH

Major Minerals

Calcium and phosphorus account for 75% by weight of the minerals. Potassium, sulfur, sodium, chlorine, and magnesium

Calcium (Ca)

Mostly in the inorganic salts of bones and teeth. In dairy, and leafy greens

Function:

Structure of bones and teeth; essential for neurotransmitter release, muscle fiber contraction, and blood coagulation; increases permeability of cell membranes; activates certain enzymes

Phosphorus (P)

Mostly in the inorganic salts of bones and teeth. Meat, cheese,nuts, dairy, legumes

Function:

Structure of bones and teeth; component in nearly all metabolic reactions; in nucleic acids, many proteins, some enzymes, and some vitamins; in cell membrane, ATP, and phosphates of body fluids

Potassium (K)

Widely distributed; tends to be concentrated inside cells. Avacado, dried apricots, meats, PB, potatoes, bananas

Function:

Helps maintain intracellular osmotic pressure and regulate pH; required for impulse conduction in neurons

Sulfur (S)

Widely distributed; abundant in skin, hair, and nails

Function:

Essential part of certain amino acids, thiamine, insulin, biotin, and mucopolysaccharides

Sodium (Na)

Widely distributed; mostly in extracellular fluids and bound to inorganic salts of bone

Function:

Helps maintain osmotic pressure of extracellular fluids; regulates water movement; plays a role in impulse conduction in neurons; regulates pH and transport of substances across cell membranes

Chlorine (Cl)

Closely associated with sodium (as chloride); most highly concentrated in cerebrospinal fluid and gastric juice

Function:

Helps maintain osmotic pressure of extracellular fluids; regulates pH; maintains electrolyte balance; forms hydrochloric acid; aids transport of carbon dioxide by red blood cells

Magnesium (Mg)

Abundant in bones

Function:

Required in metabolic reactions in mitochondria that produce ATP; plays a role in the breakdown of ATP to ADP

Trace elements

Essential nutrients needed only in minute amounts, each makes up less than 0.005% of adult body weight. Includes iron, manganese, copper, iodine, cobalt, zinc, fluorine, selenium, and chromium

Iron (Fe)

Primarily in blood; stored in liver, spleen, and bone marrow

Function:

Part of hemoglobin molecule; assists in vitamin A synthesis; incorporated into a number of enzymes

Manganese (Mn)

Most concentrated in liver, kidneys, and pancreas

Function:

Part of enzymes required for fatty acids and cholesterol synthesis, urea formation, and normal functioning of the nervous system

Copper (Cu)

Most highly concentrated in liver, heart, and brain

Function:

Most highly concentrated in liver, heart, and brain

Iodine (I)

Concentrated in thyroid gland

Function:

Essential component for synthesis of thyroid hormones

Cobalt (Co)

Widely distributed

Function:

Component of cyanocobalamin; required for synthesis of several enzymes

Zinc (Zn)

Most concentrated in liver, kidneys, and brain

Function:

Component of enzymes involved in digestion, respiration, bone metabolism, liver metabolism; necessary for normal wound healing and maintaining skin integrity

Fluorine (F)

Primarily in bones and teeth

Function:

Component of tooth enamel

Selenium (Se)

Concentrated in liver and kidneys

Function:

Component of certain enzymes

Chromium (Cr)

Widely distributed

Function:

Essential for use of carbohydrates

A

Adequate diets

provides sufficient energy as well as adequate supplies of essential nutrients to support growth, repair, and maintenance of tissues

Protein requirements

Some **dietary proteins** supply **essential amino acids**, and **nitrogen** for synthesizing nonessential amino acids

Protein usage

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•Enzymes that control metabolic rates

•Clotting factors

•The keratin of skin and hair

•Elastin and collagen of connective tissue

•Plasma proteins that regulate water balance

•The muscle components actin and myosin

•Hormones

•Antibodies that protect against infection

•They may also supply energy after digestion breaks them down

Protein

Consist of 20 different amino acids. Have a variety of functions in cells and in body (enzymes, hormones, antibodies, clotting factors, etc.)

Protein sources

Essential amino acids are those that cannot be produced in the body, and must be supplied in the diet

Animal sources of protein

contain **complete proteins**, which contain all **essential amino acids** (8 in adults, 10 in children)

Plant sources of protein

missing one or more essential amino acids, making them **incomplete** or **partially complete proteins;** these sources should be consumed in combinations

**Lipid Requirements**

Requirements vary with habits and goals

Human diets vary widely in their lipid content

Lipid intake must be high enough to carry fat-soluble vitamins

**VLDLs, very low density lipoproteins,**

contain a large amount of triglycerides

**LDLs, low density lipoproteins**

contain a large amount of cholesterol; deliver cholesterol to the cells

**HDL, high density lipoproteins**

contain a large amount of protein

Disaccharides

milk sugar, cane sugar, beet sugar, molasses

Monosaccharides

from honey and fruits

**glycogen**

from meat

**Cellulose**

is a complex carbohydrate that humans can not digest (some is broken down by intestinal flora), but provides bulk (fiber), facilitating the movement of food through the intestine

**Macronutrients**

required in large amounts; lipids, carbohydrates, and proteins

**Micronutrients**

required in small amounts; vitamins and minerals

**Movements of the Large Intestine**

**Mixing and peristaltic movements** are similar to those of the small intestine, but slower

**gastrocolic reflex**

Peristaltic waves (mass movements) occur only 2 – 3 times during the day, after a meal, in response to the

defecation reflex

Defecation is stimulated by a **_____________,** that forces feces into the rectum where they can be expelled

Large intestine functions

Does not digest or absorb nutrients

**Mucus** is the only important secretion of the large intestine; secreted by numerous goblet cells

Mucus helps pass remaining chyme along large intestine

**Absorbs electrolytes and water**

**Large Intestinal Wall**

Has the 4 layers of Alimentary wall: Mucosa, submucosa, muscularis, and serous. Lacks villi.

Fibers of longitudinal muscle are not uniform; instead arranged in 3 bands called **teniae coli,** that extend the whole length of the colon

Large intestine consist of

Cecum, colon, rectum, and anal canal

Cecum

•a pouch at the beginning of the large intestine, with the **appendix** projecting downward from it

**Colon**

consists of the ascending, transverse, descending, and sigmoid regions

**Rectum**

a straight section of the large intestine, which lies next to the sacrum

**Anal canal**

opens to the outside as the anus; guarded by an involuntary internal anal sphincter and a voluntary external anal sphincter

Large intestine

Diameter is large, about 1.5 meters long. Begins in lower fight portion of abdominal cavity at the cecum, ascends on the right, crosses to the left side, and descends on the left. absorbs water and electrolytes, and forms and stores feces

Segmentation (S intestine)

mixing movements, In segmentation, contractile rings break up chyme and move it back and forth, mixing it and slowing its movement down the intestine

**Peristalsis**

propelling movements, Peristaltic waves are weak, and propel chyme short distances; chyme takes 3 – 10 hours to travel the length of small intestine

absorption in small intestine

**Chylomicrons** transport dietary fats to muscle and adipose tissue

The intestinal villi also absorb **water** (by osmosis) and **electrolytes** (by diffusion and active transport)

**(very low density lipoprotein)** molecules, produced by the liver, transport triglycerides synthesized from excess dietary carbohydrates; at the adipose cells, lipoprotein lipase unloads the triglycerides, leaving **(low density lipoproteins)**, consisting mainly of cholesterol

Absorption in small intestine

**Monosaccharides** are absorbed by the villi,

**Amino acids** are absorbed into the blood capillaries of the villi

**Fatty acids** and glycerol from triglycerides diffuse into the villi

Secretion of small intestine

**Watery fluid:** carries digestive products into the villi, secreted by i**ntestinal glands** at the bases of the villi

**Enzymes:**  secreted by epithelial cells of the mucosa, and embedded in their microvilli

**Three organs in small intestine**

Duodenum, Jejunum, ileum

**Duodenum:**

the shortest and most fixed portion of the small intestine; the stomach empties chyme directly into the duodenum

**Jejunum**

makes up the proximal two-fifths of the small intestine, has a slightly larger diameter than the ileum, and is more active in the digestion process

**Ileum**

most distal portion of small intestine

Mesentery

The jejunum & ileum are suspended from the posterior abdominal wall by a double-layered fold of peritoneum called

**Greater omentum**

drapes over the intestine; it is a double fold of peritoneal membrane

Small intestine functions

•Receives chyme from stomach

•Receives pancreatic juice from pancreas and bile from liver and gallbladder

•Finishes digestion of nutrients that arrive in the chyme

•Absorbs digestive end products

Transports the remaining residue to the large intestine

Small intestine

a long tubular organ, which runs from the stomach to the beginning of the large intestine

Bile salt

certain digestive enzymes break down fat molecules, accomplish emulsification which involves breaking down large fat globules, aid in absorption of fatty acids, cholesterol, and fat soluble vitamins

Secretin

located in duodenal wall. Stimulates pancreas to secrete fluid with a high bicarbonate ion concentration

Gallbladder

a pear-shaped sac on the inferior surface of the liver,

**Stores bile** between meals and reabsorbs water to **concentrate the bile**

Bile

•A yellowish-green liquid that hepatic cells secrete continuously

•Composed of water, bile salts, bile pigments, cholesterol, and electrolytes

pigments (bilirubin and biliverdin) are breakdown products of hemoglobin from worn out red blood cells

Liver functions

Responsible for many **metabolic activities**, such as the metabolism of carbohydrates, lipids, and proteins

Maintains proper blood concentrations of glucose and other nutrients

Stores glycogen, vitamins A, D, and B12, and iron

Liver functions

Synthesizes lipoproteins, phospholipids, and cholesterol

Converts excess carbohydrates and proteins to fat

Deaminates amino acids, forming urea