Chapter 38-Digestive and Excretory Systems
Nutrients
-Scientists refer to the energy stored in food as Dietary Calories
-The nutrients that the body needs are water, carbohydrates, fats,
proteins, vitamins, and minerals
-Water is the most important nutrient because every cell needs it for
the body’s processes, makes up the bulk of blood, lymph and other
bodily fluids
-Carbohydrates are the main source of energy for the body, simple
carbohydrates do not need to be broken down, and complex
carbohydrates must be broken down before they can be used by the
body
-Fats are formed from fatty acids and glycerol, they help the body
produce cell membranes, myelin sheaths, certain hormones, and they
also help absorb fat-soluble vitamin
-Saturated fats and unsaturated fats
-Proteins supply raw materials for growth and repair of structures
such as skin and muscles
-Vitamins are organic molecules that help regulate body processes
-Minerals also involved in growth, energy production, and formation
Digestion
-Digestive system includes: the mouth, pharynx, esophagus,
stomach, small intestines, and large intestines. Several major
accessory structures including the salivary glands, the pancreas, and
the liver add secretions to the digestive system
The function of each organ of the digestive system is to help convert
foods into simpler molecules that can be absorbed and used by the
cells of the body
Mouth- food is broken down into chewable and swallowable chunks
by the teeth and the tongue. The teeth do much of the mechanical
digestion by cutting, tearing, and crushing food into smaller
fragments. The salivary glands secrete saliva, which helps to moisten
food and make it easier to chew. Amylase is an enzyme that breaks
down chemical bonds between the sugar monomers and the starches
Pharynx- the food then passes from the mouth or oral cavity into the
pharynx. Once in the pharynx swallowing becomes involuntary. The
medulla is the part of the brain that controls swallowing
Esophagus- food is then passed through the food tube or esophagus
and into the stomach. The food moves down the esophagus by
involuntary muscle contractions known as peristalsis. The sphincter
closes the esophagus after food passes into the stomach and
prevents contents from moving back up.
Stomach- Food enters the stomach from the esophagus. The
stomach contains microscopic gastric glands that release mucus,
hydrochloric acids, and gastric juices. Pepsin is also produced,
especially useful for protein digestion.
-Ulcers are lesions of the digestive tract lining
-The semi-liquid mass of partially digested food known as chime
enters the duodenum and into the small intestines.
Pancreas-The presence of chime in the duodenum causes the
release of pancreatic fluid from the pancreas. The pancreas is a
gland formed by the duodenum and under the surface of the
stomach. The pancreas produces hormones that regulate blood
sugar levels, produces enzymes that break down carbohydrates,
proteins, lipids, and nucleic acids, and also produces sodium
bicarbonate.
Liver-assists the pancreas, produces bile. Bile helps neutralize they
chyme from the stomach and emulsifying fats. Bile is stored in the
gall bladder.
Small Intestine-made up by the duodenum, jejunum, and the ileum,
specially adapted to absorb nutrients because it is covered with
projections called villi.
The Large Intestine-main job is to reabsorb water and electrolytes
-Diarrhea occurs when there is interference with water absorption
The Excretory System
The skin, lungs, and kidneys along with their associated organs make
up the excretory system.
The Kidneys- The main organ of the excretory system are the two
kidneys, which are located on either side of the spinal column near
the lower back. A tube called the ureter leaves each kidney, carrying
urine to the urinary bladder. The urinary bladder stores urine before
being excreted. As blood travels through the kidney, urea, excess
water, and other waste products are removed and collected as urine.
Structure of the KidneysNephron-structural and functional unit of the kidney which
manufactures urine
Glomerulus-network of capillaries which constitutes part of a single
nephron
Bowmans capsule-double walled chamber which surrounds the
glomerulus
Proximal tubule-segment of the nephron tubule where water, sodium
ions, glucose, and amino acids are absorbed into the wall
Loop of Henle- the proximal tubule leads into the loop of henle where
sodium ions are actively transported outs of the segment
Distal tubule-additional sodium can be reabsorbed out by the distal
tubule. Water is also reabsorbed here.
Collecting tubule-receives urine form smaller tubules.
Urine flows to the outside from the bladder through a tube called the
urethra
The kidneys play an important role in maintaining homeostasis. They
regulate the water content of the blood and, therefore, blood volume,
maintain blood pH, and remove waste products from the blood.
Humans can survive with one kidney, but if both are damaged by
disease or injury there are two ways to keep an individual alive. First
is a kidney transplant from a healthy, compatible donor or second
kidney dialysis.