16.3 Digestive and Excretory Systems
4 min read•august 7, 2024
The digestive system breaks down food into usable nutrients. It includes organs like the and intestines, which work together to process what we eat. Enzymes play a crucial role, breaking complex molecules into simpler forms our bodies can absorb.
The excretory system removes waste and maintains balance in our bodies. are the stars here, filtering blood and producing . They're made up of tiny units called that do the heavy lifting of waste removal and water balance.
Digestive System
Digestive Tract and Enzymes
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- The digestive system consists of the gastrointestinal tract (, , stomach, , , , ) and accessory organs (, , , )
- The digestive tract is a long, continuous tube that breaks down food into smaller molecules that can be absorbed and used by the body
- Enzymes are that act as biological catalysts to speed up chemical reactions in the body
- Digestive enzymes break down macromolecules (, proteins, ) into smaller molecules that can be absorbed by the body
- Examples of digestive enzymes include (breaks down carbohydrates), (breaks down proteins), and (breaks down lipids)
Stomach and Small Intestine
- The stomach is a muscular organ that stores and breaks down food using strong muscular contractions and acidic gastric juices
- The stomach lining secretes and (inactive form of pepsin) which help to break down food and kill bacteria
- The small intestine is a long, narrow tube (about 20 feet long) where most of the digestion and absorption of nutrients occurs
- The small intestine has three sections: (receives chyme from stomach and secretions from liver and pancreas), (middle section where most nutrient absorption occurs), and (final section that absorbs remaining nutrients and salts)
- The inner lining of the small intestine has many finger-like projections called which increase the surface area for nutrient absorption ( on the surface of each villus further increase surface area)
Large Intestine and Liver
- The large intestine (colon) is a wider, shorter tube (about 5 feet long) that absorbs water and electrolytes from the remaining digestive material and forms solid waste (feces)
- The large intestine has four sections: (connects to ileum and appendix), , , and (which leads to the rectum and anus)
- The liver is the largest internal organ and has many important functions, including producing bile (helps digest fats), storing glucose as , and detoxifying harmful substances
- The liver receives blood from the digestive tract via the hepatic portal vein, processes the nutrients and toxins, and sends the filtered blood to the heart via the hepatic veins
- The gallbladder stores and concentrates bile produced by the liver, and releases it into the duodenum when needed to digest fatty foods
Excretory System
Kidneys and Nephrons
- The excretory system removes waste products from the body and maintains homeostasis of water, salt, and pH levels in the blood
- The kidneys are a pair of bean-shaped organs located in the lower back that filter the blood and produce urine
- Each kidney contains about 1 million tiny units called nephrons
- Each nephron consists of a ( and ) and a (, , , and )
- The glomerulus is a cluster of capillaries that filters the blood under high pressure, allowing small molecules (water, glucose, amino acids, ) to pass into the Bowman's capsule while retaining larger molecules (proteins, blood cells)
Urine Formation and Homeostasis
- The filtrate from the Bowman's capsule flows through the renal tubule, where useful substances (glucose, amino acids, water, ions) are reabsorbed back into the bloodstream while waste products (urea, excess water and ions) are secreted into the tubule
- The loop of Henle creates a concentration gradient in the medulla of the kidney, allowing the kidney to produce concentrated urine and conserve water
- The distal convoluted tubule and collecting duct are regulated by hormones (, ) to fine-tune the of water and ions based on the body's needs
- The final product, urine, flows from the collecting ducts into the renal pelvis, through the ureters to the bladder, and is excreted from the body through the urethra
- The kidneys help maintain homeostasis by regulating blood volume, blood pressure, electrolyte balance, and acid-base balance through the production of urine and the secretion of hormones (, , )
Key Terms to Review (50)
Aldosterone: Aldosterone is a steroid hormone produced by the adrenal glands that plays a crucial role in regulating blood pressure and electrolyte balance in the body. It primarily acts on the kidneys to promote sodium retention, potassium excretion, and water reabsorption, thereby influencing fluid balance and blood volume. This hormone is part of the renin-angiotensin-aldosterone system (RAAS), which is vital for maintaining homeostasis in response to changes in blood pressure and volume.
Amylase: Amylase is an enzyme that catalyzes the breakdown of starch and glycogen into simpler sugars, specifically maltose and glucose. It plays a crucial role in the digestive process, beginning in the mouth and continuing in the small intestine, where it helps to convert complex carbohydrates into forms that can be easily absorbed by the body. Amylase not only aids digestion but also illustrates the importance of enzymes in facilitating biochemical reactions throughout living organisms.
Antidiuretic Hormone: Antidiuretic hormone (ADH), also known as vasopressin, is a peptide hormone produced in the hypothalamus and released by the posterior pituitary gland that helps regulate water balance in the body. By increasing water reabsorption in the kidneys, ADH plays a critical role in maintaining homeostasis, particularly during periods of dehydration or high plasma osmolality. This hormone not only impacts kidney function but also influences blood pressure by promoting vasoconstriction.
Anus: The anus is the opening at the end of the digestive tract through which solid waste is expelled from the body. It plays a crucial role in the elimination of undigested food and waste products, serving as the final component of the digestive system. The proper functioning of the anus is essential for maintaining overall health and homeostasis, as it ensures the efficient removal of waste materials from the body.
Ascending colon: The ascending colon is a section of the large intestine that travels upward on the right side of the abdomen, connecting the cecum to the transverse colon. It plays a crucial role in the digestive process by absorbing water and electrolytes from indigestible food matter, which helps form solid waste. Additionally, the ascending colon is part of the larger gastrointestinal tract, which facilitates the breakdown and absorption of nutrients while also preparing waste for elimination.
Bile: Bile is a digestive fluid produced by the liver and stored in the gallbladder, primarily responsible for the emulsification of fats in the small intestine. It plays a critical role in digestion by breaking down large fat globules into smaller droplets, which increases the surface area for enzymes to act on. This process is essential for the absorption of fat-soluble vitamins and nutrients during digestion.
Bowman's Capsule: Bowman's capsule is a cup-like structure that encases the glomerulus in the nephron of the kidney. It plays a critical role in the filtration process, as it collects the filtrate that is formed when blood is filtered through the glomerulus, allowing for the removal of waste products and excess substances from the bloodstream.
Calcitriol: Calcitriol is the active form of vitamin D in the body, crucial for regulating calcium and phosphate levels to maintain healthy bones. It is synthesized in the kidneys from its precursor, calcidiol, and plays a vital role in calcium absorption in the intestines and reabsorption in the kidneys, linking it closely to both digestive and excretory functions.
Carbohydrates: Carbohydrates are organic compounds composed of carbon, hydrogen, and oxygen, typically in a ratio of 1:2:1. They serve as a primary source of energy for the body, playing essential roles in cellular processes and metabolism. Carbohydrates can be classified into simple sugars (monosaccharides and disaccharides) and complex carbohydrates (oligosaccharides and polysaccharides), which impact digestion and nutrient absorption.
Cecum: The cecum is a pouch-like structure located at the beginning of the large intestine, connecting the ileum (the last part of the small intestine) to the colon. It plays a crucial role in the digestive process by receiving undigested food from the small intestine and serving as a site for fermentation and absorption of nutrients. The cecum also contains beneficial bacteria that aid in breaking down complex carbohydrates and fibers.
Collecting duct: The collecting duct is a critical component of the kidney's nephron responsible for the final concentration of urine. It receives filtrate from multiple nephrons and plays a vital role in water reabsorption and electrolyte balance, influenced by hormones such as antidiuretic hormone (ADH) and aldosterone. This structure helps to regulate the body's fluid balance and waste elimination effectively.
Descending Colon: The descending colon is a section of the large intestine that travels downward on the left side of the abdomen, connecting the transverse colon to the sigmoid colon. It plays a crucial role in the absorption of water and electrolytes from indigestible food matter, transforming liquid waste into a more solid form before it is stored in the rectum for eventual elimination. This section of the colon is essential for maintaining fluid balance in the body and supports overall digestive health.
Detoxification: Detoxification is the biological process through which harmful substances, toxins, and waste products are removed from the body. This process primarily takes place in the liver, which metabolizes toxins into less harmful substances that can be excreted through urine or bile. The effectiveness of detoxification is crucial for maintaining overall health and well-being, as it prevents the accumulation of toxic substances that could disrupt bodily functions.
Distal convoluted tubule: The distal convoluted tubule (DCT) is a segment of the nephron in the kidney that follows the loop of Henle and precedes the collecting duct. This tubular structure is crucial for the reabsorption of sodium, chloride, and water, as well as the secretion of potassium and hydrogen ions, playing a key role in regulating electrolyte balance and blood pressure.
Duodenum: The duodenum is the first section of the small intestine, immediately following the stomach. It plays a critical role in digestion by receiving chyme from the stomach and secretions from the pancreas and liver, allowing for the breakdown and absorption of nutrients. The duodenum is key to regulating the flow of digestive juices and ensuring that food is processed efficiently before moving into the jejunum, the next part of the small intestine.
Erythropoietin: Erythropoietin is a glycoprotein hormone produced primarily by the kidneys that stimulates the production of red blood cells in the bone marrow. This hormone plays a critical role in regulating erythropoiesis, especially in response to low oxygen levels in the blood, ensuring that tissues receive adequate oxygen supply. The regulation of erythropoietin is influenced by various factors, including blood oxygen concentration and certain hormones.
Esophagus: The esophagus is a muscular tube that connects the throat (pharynx) to the stomach, playing a crucial role in the digestive system. It transports food and liquids that have been swallowed from the mouth to the stomach through coordinated muscle contractions known as peristalsis. The esophagus is lined with a mucous membrane that protects it from the passage of food, and its structure is designed to facilitate this process efficiently.
Filtration: Filtration is the process of separating solids from liquids or gases using a filter medium that allows only certain substances to pass through. This mechanism is crucial in various biological systems, particularly for the elimination of waste products and the retention of essential substances, playing a vital role in maintaining homeostasis within the body.
Gallbladder: The gallbladder is a small, pear-shaped organ located beneath the liver that stores and concentrates bile produced by the liver. It plays a crucial role in digestion, particularly in the emulsification and absorption of fats. When fatty foods enter the small intestine, the gallbladder releases bile through the bile ducts to aid in digestion.
Glomerulus: The glomerulus is a network of tiny blood vessels located within the kidney that plays a critical role in filtering blood to form urine. It is surrounded by Bowman's capsule and is part of the nephron, the functional unit of the kidney. The primary function of the glomerulus is to allow water, ions, and small molecules to pass through while retaining larger molecules and cells in the bloodstream, which is essential for maintaining homeostasis in the body.
Glycogen: Glycogen is a multi-branched polysaccharide that serves as a form of energy storage in animals and fungi, primarily found in the liver and muscle tissues. It acts as a crucial carbohydrate reserve that the body can quickly mobilize when energy is needed, linking it closely to metabolism and energy management.
Hydrochloric acid: Hydrochloric acid is a strong, colorless acid composed of hydrogen and chlorine, with the chemical formula HCl. It plays a crucial role in the digestive system, primarily within the stomach, where it helps to break down food, activate digestive enzymes, and create an acidic environment for optimal digestion.
Ileum: The ileum is the final and longest segment of the small intestine, connecting to the cecum of the large intestine. It plays a crucial role in the digestion and absorption of nutrients, particularly vitamin B12 and bile salts, and helps to further break down food particles before they enter the large intestine. The ileum is lined with specialized structures, including villi and microvilli, which increase its surface area for maximum nutrient absorption.
Jejunum: The jejunum is the middle section of the small intestine, located between the duodenum and the ileum. It plays a crucial role in the digestion and absorption of nutrients from food, making it essential for overall digestive health. The jejunum has a large surface area due to its numerous folds and villi, which enhance nutrient absorption, and is also rich in blood supply, allowing for efficient nutrient transport into the bloodstream.
Kidneys: Kidneys are vital organs in vertebrates that play a key role in filtering blood, removing waste products, and regulating fluid balance, electrolyte levels, and blood pressure. They maintain homeostasis by producing urine to eliminate excess substances and toxins from the body. Their structure and function vary among species, reflecting adaptations to different environments and lifestyles.
Large intestine: The large intestine is the final part of the digestive system, responsible for absorbing water and electrolytes from indigestible food matter and compacting waste into feces. It plays a crucial role in maintaining hydration and the balance of electrolytes, while also housing beneficial bacteria that aid in fermentation and the production of certain vitamins.
Lipase: Lipase is an enzyme that catalyzes the breakdown of fats into fatty acids and glycerol, playing a crucial role in lipid digestion. It is primarily produced in the pancreas and secreted into the small intestine, where it works to emulsify dietary fats, making them easier for other enzymes to further digest. This process is essential for nutrient absorption and energy production within the body.
Lipids: Lipids are a diverse group of hydrophobic molecules that are essential for various biological functions, including energy storage, cellular structure, and signaling. They include fats, oils, waxes, and steroids, which play vital roles in the body's digestive processes and overall metabolism.
Liver: The liver is a vital organ in the body that performs numerous essential functions, including the production of bile, metabolism of nutrients, detoxification of harmful substances, and storage of vitamins and minerals. It plays a central role in the digestive system by processing nutrients absorbed from the intestines and ensuring the body maintains proper chemical balance.
Loop of Henle: The loop of Henle is a U-shaped portion of the nephron in the kidney that plays a critical role in concentrating urine and maintaining the body's water and salt balance. It consists of a descending limb that permeates water and an ascending limb that actively transports sodium and chloride ions out of the filtrate, which contributes to the countercurrent multiplication mechanism essential for creating concentrated urine. This structure connects the proximal convoluted tubule and the distal convoluted tubule, making it vital for kidney function and overall homeostasis.
Microvilli: Microvilli are small, finger-like projections that extend from the surface of epithelial cells, significantly increasing their surface area. These structures are particularly abundant in the intestines, where they enhance nutrient absorption by providing a larger area for interaction with digested food. Microvilli are crucial for efficient digestion and play a role in the overall functioning of the digestive system.
Mouth: The mouth is the opening in the face of humans and many animals that serves as the entry point for food and the start of the digestive process. It plays a critical role not only in digestion but also in speech and breathing, as it houses structures like teeth, gums, and the tongue that aid in breaking down food and mixing it with saliva, which contains enzymes that initiate digestion.
Nephrons: Nephrons are the functional units of the kidneys responsible for filtering blood and producing urine. Each kidney contains approximately one million nephrons, which work to remove waste products and excess substances from the bloodstream, maintaining the body's fluid and electrolyte balance. They consist of several components that facilitate the filtration process, including the glomerulus and renal tubule, making them essential in the excretory system.
Pancreas: The pancreas is a vital organ that plays a crucial role in both the digestive and endocrine systems. It produces digestive enzymes that help break down food in the small intestine, as well as hormones like insulin and glucagon that regulate blood sugar levels. This dual functionality makes the pancreas essential for maintaining overall metabolic balance and digestive health.
Pepsin: Pepsin is a digestive enzyme produced in the stomach that breaks down proteins into smaller peptides. It plays a crucial role in the digestive process by initiating the breakdown of proteins, which is essential for nutrient absorption. Pepsin is secreted as an inactive precursor called pepsinogen, which is activated by the acidic environment of the stomach.
Pepsinogen: Pepsinogen is an inactive precursor to the digestive enzyme pepsin, secreted by the chief cells in the stomach lining. Once released into the acidic environment of the stomach, pepsinogen is activated into pepsin, which plays a crucial role in breaking down proteins into smaller peptides during digestion.
Proteins: Proteins are large, complex molecules made up of long chains of amino acids, essential for the structure, function, and regulation of the body's tissues and organs. They play a crucial role in various biological processes, including digestion, as they help break down food into absorbable nutrients, and in the excretory system, where they aid in the elimination of waste products from the body.
Proximal Convoluted Tubule: The proximal convoluted tubule (PCT) is a critical segment of the nephron in the kidney, responsible for the reabsorption of essential nutrients, ions, and water from the filtrate back into the bloodstream. It plays a significant role in regulating the body’s fluid balance and electrolyte levels, contributing to overall homeostasis. Located just after the Bowman’s capsule, the PCT is lined with microvilli that increase surface area for efficient absorption.
Reabsorption: Reabsorption is the process by which substances in the filtrate produced by the kidneys are transported back into the bloodstream. This crucial function helps maintain the body's fluid and electrolyte balance by ensuring that essential nutrients, ions, and water are conserved, preventing their loss in urine. It occurs primarily in the renal tubules of the nephrons, where specific transport mechanisms facilitate the selective recovery of substances.
Rectum: The rectum is the final section of the large intestine that serves as a temporary storage site for feces before they are expelled from the body. It plays a crucial role in the excretory system by facilitating the elimination of waste. The rectum is equipped with stretch receptors that signal when it is full, prompting the urge to defecate, and is surrounded by sphincter muscles that control the release of feces.
Renal Corpuscle: The renal corpuscle is the initial filtering component of the nephron in the kidney, consisting of the glomerulus and Bowman's capsule. It plays a crucial role in the excretory system by filtering blood to form urine, allowing waste products and excess substances to be removed while retaining essential components like proteins and blood cells.
Renal tubule: The renal tubule is a component of the nephron in the kidney that is responsible for the reabsorption and secretion of various substances during urine formation. This structure consists of several segments, including the proximal convoluted tubule, loop of Henle, distal convoluted tubule, and collecting duct, which work together to process filtrate and maintain homeostasis in the body by regulating water, electrolytes, and waste products.
Renin: Renin is an enzyme secreted by the kidneys that plays a critical role in the regulation of blood pressure and fluid balance in the body. It initiates the renin-angiotensin-aldosterone system (RAAS), which is essential for maintaining homeostasis. When blood pressure drops or there is a decrease in sodium chloride, renin is released into the bloodstream to trigger a cascade of reactions that ultimately raise blood pressure and increase blood volume.
Salivary glands: Salivary glands are exocrine glands located in and around the oral cavity that produce and secrete saliva, a digestive fluid crucial for the initial stages of digestion. They play a vital role in moistening food, aiding in taste perception, and providing enzymes that begin the breakdown of carbohydrates. The secretion of saliva also helps maintain oral hygiene by neutralizing acids and washing away food particles.
Small intestine: The small intestine is a long, coiled tube that connects the stomach to the large intestine and is crucial for digestion and nutrient absorption. It is where most of the digestion of food occurs, aided by enzymes and bile, allowing the body to absorb vitamins, minerals, and other nutrients effectively.
Stomach: The stomach is a muscular organ in the digestive system that plays a crucial role in breaking down food through mechanical and chemical processes. It acts as a temporary storage space where food is mixed with gastric juices, including hydrochloric acid and enzymes, to facilitate digestion before it moves into the small intestine. The stomach also has specialized cells that produce mucus to protect its lining from the acidic environment.
Transverse colon: The transverse colon is the part of the large intestine that crosses the abdomen from right to left. It connects the ascending colon on the right side of the body to the descending colon on the left, playing a vital role in the digestive system by facilitating the movement of waste material and absorption of water and nutrients.
Urea: Urea is a nitrogenous compound produced in the liver as a waste product of protein metabolism, primarily excreted through urine. It plays a vital role in the excretory systems of many animals, allowing them to safely eliminate excess nitrogen from the body. The process of urea synthesis and excretion is crucial for maintaining nitrogen balance and preventing toxicity from ammonia, especially in organisms that have evolved to conserve water.
Urine: Urine is a liquid waste product produced by the kidneys through the filtration of blood. It plays a crucial role in the excretory system by removing excess substances, such as urea, creatinine, and various ions, which helps maintain the body's internal balance of fluids and electrolytes. The composition and volume of urine can provide insights into an individual's hydration status, metabolic processes, and overall health.
Villi: Villi are small, finger-like projections that extend from the surface of the intestinal lining, particularly in the small intestine. They play a crucial role in nutrient absorption by increasing the surface area available for absorption, allowing for more efficient transfer of nutrients into the bloodstream. Villi contain specialized cells that facilitate the uptake of nutrients, making them essential for proper digestion and overall health.