The Digestive and Excretory Systems What goes in, must come out…
The Digestive System • The food you eat contains nutrients, fats, proteins, carbohydrates, vitamins and minerals • Most of these molecules are too big to pass through the cell membrane… • That’s where the digestive system comes in… • The process of breaking food molecules into smaller molecules is called digestion.
Digestion • Digestion starts out with mechanical digestion in the mouth • Some chemical digestion • saliva contains amylases that break down carbohydrates • When you swallow, food passes into the esophagus • moved along by wavelike contractions called peristalsis
More digestion • Food then moves into the stomach • acids break down proteins • the food continues to get mixed and mechanically broken down • Food passes from the stomach into the small intestine • The small intestine is the location that most of the chemical digestion takes place
The small intestine • Secretions from the pancreas, liver, and gall bladder enter the small intestine and complete the digestion of fats, proteins, and carbohydrates • The nutrients from these molecules are absorbed by the lower parts of the small intestine
The large intestine • As food leaves the small intestine, most of the nutrients have been absorbed • No digestion takes place in the large intestine, but water and mineral ions are absorbed • The large intestine is also the place where bacteria produce vitamin K and vitamin B that you cannot easily get from the food you eat
The excretory system • Any organ that excretes wastes is part of the excretory system (skin, lungs, large intestines) • However, for our purposes, we will focus most of our discussion on the elimination of urine
The urinary system • Kidneys filter water soluble wastes from the blood and they eliminate excess water from the body…they also reabsorb water so that we don’t lose too much • The urine produced then passes into the ureters…the tubes that lead to the bladder • The bladder holds the urine • The urine then exits the body through the urethra
Other wastes • Wastes left over from food are removed by the • Colon (large intestine) • Excess salt and water are removed by the kidneys and also the (Hint: sweat) • Skin!
More • When we take in chemicals that might be toxic (like the metabolites of alcohol), our _____ filters these poisons from our blood • Liver • Carbon dioxide builds up in our tissues and is removed from the cells by ___ and our bodies by _____ • Our blood • Our lungs
Relationships • What other systems are dependent on our digestive system and why? • All of them! The digestive system breaks down food to provide nutrients to ALL of the body systems! • What other systems are dependent on our excretory system? • All of them! Wastes build up… what goes in must come out!!! (or we’d be full of poop and poison)
More relationships • What system helps our digestive system deliver nutrients and our excretory system pick up wastes? • The circulatory system! • What system is involved in removing waste gases? • The respiratory system!