Chapter 3 - Cells

The bodies cells

cells need energy, oxygen, water and nutrients to do their work.

Genes determine the nature of cells work and affect how nutrients are handled.

cells -> tissues -> organs -> body system

tissues

systems of cells working together to perform specialized tasks.

Examples are muscles, nerves, blood, and bone.

organs

discrete structural units made of tissues that perform specific jobs.

Example are the heart, liver, and brain.

body system

a group of related organs that work together to perform a function.

Examples are the circulatory system, respiratory system, and nervous system.

enzyme

any of a great number of working proteins that speed up a specific chemical reaction such as breaking the bonds of a nutrient, without undergoing change themselves.

fat cells

cells that specialize in the storage of fat and form the fat tissue.

Fat cells also produce fat-metabolizing enzymes;

they also produce hormones involved in appetite and energy balance

inborn error of metabolism

a genetic variation present from birth that may result in disease.

ex - phenylketonuria - interferes with the body’s handling of the amino acid phenylalanine, with potentially serious consequences for the brain and nervous system in infancy and childhood.

blood circulation

All the blood circulates to the lungs, where it picks up oxygen and releases carbon dioxide wastes from the cells.

Then the blood returns to the heart, where the pumping heartbeats push this freshly oxygenated blood from the lungs out to all body tissues.

As the blood travels through the rest of the cardiovascular system, it delivers materials cells need and picks up their wastes.

blood circulation to the intestine

AS it passes through the digestive system, the blood delivers oxygen to the cells there and picks up most nutrients other than fats and their relatives from the intestine for distribution elsewhere.

Lymphatic vessels pick up most fats from the intestine and then transport them to the blood.

All blood leaving the digestive system is routed directly to the liver, which has the special task of chemically altering the absorbed materials to make them better suited for use by other tissues.

Later, in passing through the kidneys, the blood is cleansed of wastes

Transport of nutrients

body fluids supply tissues with nutrients.

transported through blood and lymph nodes

blood nutrient transport

carries water soluble nutrients, goes from small intestine to liver to heart.

arteries carry oxygen and nutrients to tissues and blood circulates among cells by capillaries.

it exchanges of materials between the cell fluid and the extracellular fluid by delivering oxygen and nutrients and picking up carbon dioxide and wastes and this returns to the heart via veins and the carbon is removed by the lungs in exchange for oxygen.

blood also circulates to the kidneys where wastes are removed (filtered by nephrons) and excreted in urine

Lymph nutrient transport

carries fat soluble nutrients.

goes from small intestine via the lymphatic system to teh thoracic duct where lymph enters the bloodstream near the heart "oil mixing with water"

regulation

communication between organs and cells.

done through - hormones and nervous system and sometimes both

hormones

chemicals that are secreted by glands into the blood in response to conditions in the body that require regulation.

These chemicals serve as messengers, acting on other organs to maintain constant conditions. For example, when the pancreas (a gland) detects a high concentration of the blood’s sugar, glucose, it releases insulin, a hormone.

Insulin stimulates muscle and other cells to remove glucose from the blood and to store it. The liver also stores glucose.

When the blood glucose level falls, the pancreas secretes another hormone, glucagon, to which the liver responds by releasing into the blood some of the glucose it stored earlier. Thus, a normal blood glucose level is maintained.

hormone functions

• Carry messages to regulate the digestive system in response to meals or fasting,

• Inform the brain about the degree of body fatness,

• Help to regulate hunger and appetite,

• influence appetite changes during a woman’s menstrual cycle and in pregnancy.

• Regulate the body’s reaction to stress, suppressing hunger and digestion.

nervous system

responds to need for food (hunger), regulates digestion (gastric juices). The nervous system’s role in hunger regulation is coordinated by the brain. The sensations of hunger and appetite are perceived by the brain’s cortex.

the hypothalamus monitors many body conditions, including the availability of nutrients and water.

To signal hunger, the physiological need for food, the digestive tract sends messages to the hypothalamus by way of hormones and nerves. The signals also stimulate the stomach to intensify its contractions and secretions, causing hunger pangs.

When your brain’s cortex perceives these hunger sensations, you want to eat. The conscious mind of the cortex, however, can override such signals, and a person can choose to delay eating despite hunger or to eat when hunger is absent.

combo of hormones and nervous system

flight or flight reaction, epinephrine and body responses and movements.

When danger is detected, nerves release neurotransmitters, and glands supply the compounds epinephrine and norepinephrine.

Every organ of the body responds, and metabolism speeds up. The liver pours forth glucose from its stores, and the fat cells release fat.

The digestive system shuts down to permit all the body’s systems to serve the muscles and nerves.

Immune system

Many of the body’s tissues cooperate to maintain defenses against infection, and all these tissues depend on an ample supply of nutrients to function properly.

The skin presents a physical barrier, and the body’s cavities (lungs, mouth, digestive tract, and others) are lined with membranes that resist penetration by invading microbes and other unwanted substances.

These linings are highly sensitive to vitamin and other nutrient deficiencies, and health-care providers inspect both the skin and the inside of the mouth to detect signs of malnutrition.

why do we like sugar, fatty and salty foods?

The enjoyment of sugars is in born and encourages people to consume ample energy, especially in the form of foods containing carbohydrates, which provide the energy fuel for the brain.

The aversion to bitterness, universally displayed in infants, discourages consumption of potentially dangerous substances containing bitter toxins and also affects people’s food preferences later on.

digestion

the breakdown of nutrients into their smallest subunits for absorption into the body. the mouth help taste buds guide food acceptability.

CHO - monosaccharides,

protein - amino acids,

Fat - fatty acids and glycerides.

2 kinds of digestion - mechanical and chemical

mechanical digestion

chew and mix food with saliva (mucus and enzymes).

Once food has been mashed and moistened for comfortable swallowing, longer chewing times provide no additional advantages to digestion.

The stomach and intestines then take up the task of liquefying foods through various mashing and squeezing actions (peristalsis)

chemical digestion

salvia contains salivary amylase enzyme to begin breakdown of CHO.

enzyme in saliva starts rapidly breaking down starch, and another enzyme initiates a little digestion of fat, especially the digestion of milk fat (important in infants). Saliva also helps maintain the health of the teeth in two ways by washing away food particles that would other wise foster decay and by neutralizing decay-promoting acids produced by bacteria in the mouth

esophagus

passes food to the stomach via peristalsis (wave like muscular squeezing along digestive tract)

stomach in mechanical

churns and mixes food into liquid mass (chyme).

Movement is aided by 3 layers of muscle along the GI tract.

controlled by - cardiac sphincter (into stomach), pyloric valve (into small intestine).

The starches have been partly split, proteins have been uncoiled and clipped, and fat has separated from the mass.

The muscular pyloric valve at the stomach’s lower end controls the exit of the chyme, allowing only a little at a time to be squirted forcefully into the small intestine.

stomach in chemical

adds hydrochloric acid and enzymes (pepsin to breakdown proteins) and fluids (gastric juice, PH is 2 to denature proteins, kill microorganisms, and mucus to protect the stomach wall ).

In the stomach, protein digestion begins. Cells in the stomach release gastric juice, a mixture of water, enzymes, and hydrochloric acid. this is needed to activate a protein-digesting enzyme and to initiate digestion of protein—protein digestion is the stomach’s main function.

specialized cells secrete a thick, viscous substance known as mucus, which coats and protects the digestive tract lining.

heartburn

burning sensation in the chest caused by backflow of stomach acid into the esophagus. antacids for temporary relief

small intestine in mechanical

segmentation.

bile emulsifies fat to assist digestion which is synthesized in the liver, stored in gallbladder and enters the small intestine via bile duct.

The small intestine contracts rhythmically to move the contents along its length.

small intestine in chemical

20 feet long, pancreas secretes bicarbonate (insulin and glucagon) that neutralizes the acidic contents from the stomach. enzymes from pancreas and small intestine digest CHO (p. amylase), protein (p. chymotrypsin) and fat (lipase).

As the thoroughly liquefied and partially digested nutrient mixture arrives there, hormonal messengers signal the gallbladder to contract and to squirt the right amount of bile, an emulsifier, into the intestine. Other hormones notify the pancreas to release pancreatic juice, containing the alkaline compound bicarbonate, in amounts precisely adjusted to neutralize the stomach acid that has reached the small intestine.

The cells of the intestinal wall also hold some digestive enzymes on their surfaces; these enzymes perform last-minute breakdown reactions required before nutrients can be absorbed.

Finally, the digestive process releases pieces small enough for the cells to absorb and use. Digestion by human enzymes and absorption of carbohydrate, fat, and protein are essentially complete by the time the intestinal con tents enter the colon. Water, fiber, and some minerals, however, remain in the tract.

microbes in digestive tract

contains 100 trillion microbiota, which do many things in the digestive tract and can effect our bodies in many ways. Digestive tract bacteria harvest energy from undigested food substances and use it to sustain themselves and to proliferate. In the process, they yield smaller molecules that the body can absorb and use. examples - Ferment many indigestible fibers, producing short fatty acids that provide many colon cells with most of their needed energy, Break down any undigested protein or unabsorbed amino acids that reach the colon, producing ammonia and other compounds, Break down and help to recycle components of bile and Chemically alter certain drugs and phytochemicals, changing their effects on the body. Bacteria produce several vitamins, too, but in amounts insufficient to meet the body’s needs, so these vitamins must be obtained from the diet. Diet strongly influences the composition and metabolism of the intestinal bacteria, onsume an adequate diet of mostly whole foods to provide the fiber upon which beneficial bacteria can thrive.

absorption

movement of nutrients from small intestine into the blood (water soluble nutrients, goes to the liver) or lymph (fat soluble to go to the blood vessel near heart). large absorptive area created by folds of vili and smaller projections of micro villi. what is not absorbed (fibre) strays in small intestine and passes into large intestine (colon).  Each villus (projection) has its own capillary network and a lymph vessel, so that, as nutrients move across the cells, they can immediately mingle with the body fluids. in cases of malnutrition, the villi surface can be reduced to 10th of its normal area, which prevents it from absorbing what few nutrients it can get. without sufficient fibre, the muscles become weak

large intestine and rectum in mechanical

mostly to reabsorb the water donated earlier by digestive organs and to absorb minerals, leaving a paste of fiber and other undigested materials, the feces, suitable for excretion. The fiber provides bulk against which the muscles of the colon can work. The rectum stores this fecal material to be excreted at intervals.

Lower GI tract

includes the large intestine and rectum. the large intestine reabsorbs water and mineral and passes wastes (fibre, bactiera or any unabsorbed nutrients) and some water to rectum. The rectum stores wastes prior to elimination

sugar and starch summary digestion

mouth - salivary glandssecrete saliva to moisten and lubricate food; chewing crushes and mixes it with a salivary enzyme that initiates starch digestion. stomach - Digestion of starch continues while food remains in the upper storage area of the stomach. In the lower digesting area of the stomach, hydrochloric acid and an enzyme in the stomach’s juices halt starch digestion. Upper GI tract - pancreas produces a starch-digesting enzyme and releases it into the small intestine. Cells in the intestinal lining possess enzymes on their surfaces that break sugars and starch fragments into simple sugars, which then are absorbed. Colon - Undigested carbohydrates reach the large intestine and are partly broken down by intestinal bacteria.

Fibre summary digestion

mouth -  teeth crush fiber and mix it with saliva to moisten it for swallowing. stomach - no action. Upper GI tract - fiber binds to cholesterol and some minerals. Colon - most fiber is excreted with feces, some fiber is digested by bacteria.

fat summary of digestion

Mouth - Fat-rich foods are mixed with saliva. The tongue produces traces of a fat-digesting enzyme that accomplishes some breakdown, especially of milk fats. The enzyme is stable at low pH and is important to digestion in nursing infants. stomach - Fat tends to rise from the watery stomach fluid an foods and float on top of the mixture. Only a small amount of fat is digested. Fat is last to leave the stomach. Upper GI - The liver secretes bile; the gallbladder stores it and releases it into the small intestine. Bile emulsifies the fat anf readies it for enzyme action. The pancreas produces fat-digesting enzymes and releases them into the small intestine to split fats into their component parts (primarily fatty acids), which then are absorbed. Colon - Some fatty materials ­escape absorption and are carried out of the body with other wastes.

protein digestion summary

mouth - Chewing crushes and softens protein-rich foods and mixes them with saliva. stomach - Stomach acid (hydro-chloric acid) works to uncoil protein strands and to activate the stomach’s protein-digesting enzyme. Then the enzyme breaks the protein strands into smaller fragments. Upper GI - Enzymes of the small intestine and pancreas split protein fragments into smaller fragments or free amino acids. Enzymes on the cells of the intestinal lining break some protein fragments into free amino acids, which then are absorbed. Some protein fragments are also absorbed. Colon - Resident bacteria break down small amounts of undigested protein and amino acids; any remaining residue is carried out of the body with the feces. Normally, almost all food protein is digested and absorbed.

water digestion summary

mouth - The mouth donates watery, enzyme-containing saliva. stomach - the stomach donates acidic, watery, enzyme containing gastric juice. Upper GI - The liver donates a watery juice containing bile. The pancreas and small intestine add watery, enzyme-containing juices; pancreatic juice is also alkaline. colon - The large intestine reabsorbs water and some minerals

Common issues affecting the digestive tract

gas and hiccups, heartburn, ulcer, diarrhea, constipation, IBS

kidneys

Though they account for just 0.5 percent of the body’s total weight, the kidneys use up 10 percent of the body’s oxygen supply, indicating intense metabolic activity. the kidneys regulate the fluid volume and concentrations of substances in the blood and extracellular fluid with great precision.

storage systems

bodies energy stories of excess energy-containing nutrients - fat in cells/adipose tissue (large amount), CHO as glycogen in liver and muscle (small amount) and other nutrients in other tissues etc bone. the liver stores excess energy containing nutrients as glycogen in body fat. fat cells of the adipose tissue pick up the remainder and store it to meet long-term energy needs. Unlike the liver, fat tissue has virtually infinite storage capacity. liver and fat cells store many vitamins, and bones provide reserves of calcium and other minerals.

Alcohol

acts as lipid solvents, easily penetrate cells outer lipid membrane, and denature cells protein structure. Alcohol in beverages in ethanol. It provides 7cal/g of energy but not a nutrient. ex - 12 oz (341ml) Beer = 150 cals ( light beer = 100 cal). Canada health guide recommends 2 standard drinks per week as more consumption increases risk of heart disease, stroke, cancers etc

Alcohol in the body

it diffuses through the stomach wall into bloodstream. food delays diffusion and stomach emptying. Vomiting protects against high dose of toxin. alcohol absorbed rapidly in small intestine (regardless of food or not). it takes about 1.5 hours to metabolize 1 drink and walking, caffeine etc do not detoxify. It is preferentially used for energy, thus more fat is stored, esp abdominal region

physical effects of alcohol

increase urine output, mineral loss. if slow drinker - it is collected by liver and processed. rapid drinker - some flows through rest of body and brain.

alcohol and the brain

it is a depressant. it sedates nerve cells. 1st - judgement and reasoning 2 - voluntary muscle control 3 - respiration and heart action. passing out helps protect against consumption of a lethal dose. note the difference between methanol and ethanol

alcohol and the liver

==the liver detoxifies (metabolizes) into 80% alcohol dehydrogenase (ADH)==, 10% MEOS system (inducible) and 10% through breath and urine. Blood alcohol is proportional to breath alcohol. some ADH in stomach (females have less). alcohol stimulates fat synthesis in the liver both acutely and chronically. this can lead to liver deterioration - fatty liver -> fibrosis (scar tissue) - > cirrhosis (loss of function

Hangover

toxic effects of congeners (other substances in alcoholic beverages). dehydration and rehydration of the brain due to brain cells loosing water, accumulation of formaldehyde (preferentially ethanol -> acetaldehyde.). Toxic to cells and increases risk for many diseases. consuming elctrolites and water assist in recovering from hangover.

longterm affects of alcohol

liver cells - amino acid metabolism, synthesis of blood lipids increases, toxic for muscle, increase BP, increased dementia risk, increase risk of cancer (mouth, esophagus etc), for younger people have an increased risk of death. fatty liver; the condition interferes with the distribution of nutrients and oxygen to the liver cells. If heavy drinking continues for long enough, fibrous scar tissue invades the liver. This is the second stage of liver deterioration, called fibrosis. Fibrosis is reversible with good nutrition and abstinence from alcohol, but the next (last) stage, cirrhosis, is not. In cirrhosis, the liver cells harden, turn orange, and die, losing function forever.

alcohol and nutrition

abuse can lead to inadequate food intake, impaired nutrient absorption and metabolism. ex - thiamin deficiency (wernickle-korsakoff syndrome).