Digestion, Circulation, and Respiration

DIGESTION, CIRCULATION, AND RESPIRATION

What: Students will learn the basic functions and processes of the digestive, circulatory, and respiratory systems.  

Why: This will give students a basic understanding of how these critical organ systems function and help sustain the life of a human being. 

How: Reading, lecture and quiz.  

Objective 1: Students will be able to discuss the process of digestion, with the organs affecting digestion in the correct order.

Objective 2: Students will be able to discuss the circulatory system, and relay understanding of circulation, heart beat, and types of cells of flow of the blood. 

Objective 3: Students will be able to discuss the respiratory system, and how blood gasses exchange.

 

 

DIGESTION

Digestive System- a tube in which food is reduced to particles, then to molecules small enough to be absorbed into the internal environment.  Human have a COMPLETE Digestive System- which means it has an opening for food to go in, and an opening at the other end for waste to be eliminated.  Some organisms have only one opening, where both nutrition goes in and waste goes out.  This is called an incomplete digestive system. 

The system is folded back and forth, but if it were stretched out it would measure  21 to 30 feet long. 

There are four functions of the digestive system:

1. Motility- muscular movements of the systems tubular walls- this movement mixes food, helps reduce its particle size, passes it along to the next organ, and finally pushes it out as eliminated waste.

2. Secretion- release of digestive enzymes and fluids

3. Digestion- breakdown of food into particles and then molecules small enough to be absorbed

4. Absorption- passage of nutrients and fluids across the tube wall and into the blood.

The Process:

1. Chewing

       A human has 32 teeth in upper and lower jaws.  The front teeth are called incisors shear/cut off chunks of food, canines tear off food, and premolars and molars grind and crush the food.  Digestive enzymes in saliva immediately begin to break down the food, and the saliva moistens it so it is easier to swallow. 

2. Swallowing

   The tongue muscles contract and the food begins to move down the pharynx ( top of the throat) contractions of the muscles around the esophagus contract and move the food down  to the stomach.

3. Stomach

     The stomach is a muscular stretchy sac. It mixes the food, dissolves and degrades the food, and helps control the passage of food to the small intestine.  Glands in the stomach secrete Hydrochloric acid, about 2 liters per day.  The mixture of acid and food is called CHYME.  The acid kills many microorganisms.   Heartburn is when the acid backs up into the esophagus. The stomach walls secrete mucous and bicarbonate ions that counter the acid. Contractions of the stomach muscle close a sphincter at the top of the small intestine.  Only a small amount of Chyme is allowed into the intestine before the sphincter closes again. 

4. Small Intestine

    Most of the nutrients from food are absorbed in the small intestine.  The pancreas and liver secret enzymes into the small intestine that help with this process.  Pancreatic enzymes break down carbohydrates, proteins, nucleic acids and fats.  It also secrets Bicarbonate which helps buffer the acidic chyme arriving from the stomach.   (Pancreatic hormones insulin and glucagon have rolls in nutrition not digestion) .  The liver secretes bile that helps with fat digestion by a process called emulsification ( breaking up fat blobs). 

5. Large Intestine

     Substances not absorbed in the small intestine move into the large intestine- also called the COLON. Here the waste is concentrated and stored.  While in the large intestine, water and ions move out of the substance and back into the blood stream.  

6. Rectum

     The waste material moves into the rectum.  Distention of the rectum wall triggers a reflex pathway for rectum muscles to contract.  

7. Anus

     The anus is a sphincter is stimulated or inhibited by the nervous system.  An older child has learned to voluntarily control this urge to expel waste.  

 

CIRCULATION

The circulatory system rapidly transports substances to and from cells.  The blood interacts with the interstitial fluid between cells, where it picks up or drops off substances.  The blood flows through vessels of various thicknesses and sizes.  The heart, a muscular pump, generates pressure to keep the blood flowing.  It is a closed system.  Blood flows faster through the big vessels, but slows down in the small vessels called capillaries.  

Blood volume is  generally 6 to 8 % of a persons body weight, averaging 4 to 6 quarts. 

THE COMPONENTS OF BLOOD:

Plasma- mostly water.  Also contains ions, molecules, and proteins

Red Blood Cells- Erythrocytes- biconcave disks- carry oxygen and some CO2 waste- Cell Count- the number of cells in a microliter of blood- 5.4 million in males, 4.8 million in females

White Blood Cells- eat old cells, cancer cells, foreign bodies, bacteria, viruses

Platelets- fragments of stem cells that last 5 to 9 days, with hundreds of thousands always circulating in the blood- they release substances that cause blood clotting

BLOOD CIRCULATION ROUTE

 

A MUSCULAR WALL DIVIDES THE HEART INTO TWO HALVES

     This division is the basis of two cardiovascular Circuits- each Circuit has its own set of arteries, arterioles, capillaries, venules, and veins.  These two circuits are called the pulmonary circuit and the systemic circuit.  

Pulmonary Circuit:

The Right side of the heart

of the heart pumps  blood to the lungs where the blood picks up oxygen and gives up carbon dioxide.  It then pumps the blood to the hearts left side.

The Left Side of the heart

pumps oxygenated blood to all the rest of the body.  When it has dropped off its oxygen to the furthest tissue, the now oxygen-poor blood is pumped back to the right side of the heart. 

 

Each half of the heart has  an ATRIUM and a VENTRICLE with one way valves to keep the blood from flowing backward.  The heart has its own circulation, feeding its muscle cells, which consists of two CORONARY ARTERIES. Each time the heart beats its four chambers first Contract- called systole and then relax called diastole.  Special muscle cells, called the SA NODE, tell the heart to beat.  They are the cardiac pacemaker.  

Blood Vessels

Arteries carry blood away from the heart.  Veins carry blood back to the heart.  Arterioles are a litte smaller than arteries, and capillaries are the smallest blood vessel. 

 

RESPIRATION

The respiratory system exchanges gasses, oxygen and CO₂

These gasses are part of the vital process of cellular respiration.  Gasses enter and leave the body by crossing a respiratory surface, in most animals a thin membrane, an  epithelial layer. Gasses need a fluid to dissolve in to diffuse across the thin membrane, so the respiratory tissues need to be moist.  Gasses diffuse across membranes on a concentration gradient. 

It takes around 300 million breaths to get you to age 75.  You can go without oxygen for only 5 minutes before your brain begins to die.  

The Process: 

The diaphragm:

The diaphragm is a large dome shaped muscle.  When it contracts it flattens out, enlarging the chest cavity, and creating negative pressure/empty space.  Air rushes into the empty space. When it relaxes gasses are expelled from the lungs. There is always some air left in the lungs.  If all the air were expelled, the alveoli would all stick together, and the lung and air could not be inhaled again...a person would not be strong enough on their own. 

Mouth and Nose:

The mouth and nose warm the air as it enters the body.  The nose and mucous membranes catch dust and particles on hairs and mucous. The air swirls a bit because of the shape of the nasal passages. 

Pharynx:

The top of the throat.  The air passes into the top of the throat from the mouth and nose.

Larynx:

The voice box.  This airway is blocked during swallowing and open during breathing. It is where sound is produced.

Trachea: 

The air passes through the larynx and into the trachea a tube leading to the bronchial tree.

Bronchial Tree:

The air passes through smaller and smaller branching's called bronchioles.

Alveolus:

Alveolus are pouches at the end of the bronchioles, little clusters of sacs, surrounded by capillaries,  where gasses are exchanged. You have about 300 million alveoli per lung. Gasses are exchanged because they move down their concentration gradient.  The alveoli have a high concentration of oxygen, and the blood has little in it, so the oxygen diffuses across the alveolar membrane and across the capillary wall, where a blood cell with hemoglobin grabs it up.  At the same time, the blood is carrying CO2, and the alveoli have very little CO2, so the CO2 diffuses across the capillary membrane, across the alveolar membrane and into the alveolar sac, where it is breathed out.