Unit 7: The digestive and urinary systems

4 primary functions (in humans)

1. nutrient acquisition: ingestion at mouth

2. digestion: breakdown into smaller pieces

3. absorption: nutrients enter bloodstream

4. excretion: getting rid of wastes

2 Names for the “Digestive System”

1. Gastrointestinal Tract (GI Tract)

2. Alimentary Canal

What is the Digestive System

a continuous tube with openings on both ends

⭐ technically, food is always outside of your body (only nutrients go in)

Structures of the GI Tract

mouth → pharynx (oro- and laryngopharynx) → esophagus → stomach → small intestine → large intestine (colon)→ rectum → anus

Digestive System also includes accessory structures:

• teeth

• tongue (papillae)

• liver (makes bile)

• pancreas (releases digestive enzymes)

• digestive glands

Activities of the Digestive System

• Ingestion: intake of food (mouth only)

• Propulsion: movement of substances

  • Voluntary: swallowing

  • Involuntary: peristalsis

• Mechanical Digestion: chewing at mouth, churning at stomach, and segmentation at intestine (physical process)

• Chemical Digestion: enzymes secreted into lumes to break down molecules

• Absorption: passage of digested end products, in addition to vitamins, minerals, and water

Muscularis Externa at Stomach (Deep → Superficial)

• oblique layer

• circular layer

• longitudinal layer

The stomach

Gastro

Textured inferior formed by ridges called rugae (sing = ruga)

• only visible when stomach is empty

• as stomach fills, rugae stretch to accomodate increased volume

Stomach Vocabulary Distinction

food leaves (mouth) →bolus leaves (stomach) → chyme leaves (rectume) → feces

Mucosa of Stomach

millions of gastric pits that lead into gastric glands

Mucus Neck

secrete mucus

Parietal Cells

secrete HCI (activates digestive enzymes)

Chief Cells

release pepsinogen (when activated by HCI pepsinogen is converted to pepsin a digestive enzyme)

Enteroendocrine

secrete hormones

Pepsinogen (chief) + HCI (parietal) =

pepsin (digestive enzyme that breaks down protein)

Peristalsis

involuntary propulsion (smooth muscle)

Steps of Peristalsis

1. circular muscle “behind” mass (bolus/chyme/feces) contracts

2. circular muscle “below” the mass relaxes fully

3. longitudinal muscles below mass contract (“gathering”) to shorten tube and move mass

4. process repeats

The Two Types of Intestines

small and large

Small Intestine

• duodenum (~1ft)

• jejunum (~8ft)

• ilium (~12ft)

Large Intestine

• cecum

• ____ colon (x4)

Gastric contractions push material towards the lowest

pyloris (3/min when stomach is full)

Pyloric sphincter controls the amount of ____ allowed into the duodenum at a time

chyme (~3mL per opening)

Structure and function relationship of the small intestine with villi and microvilli

1. circular folds

2. intestinal crypts

Circular folds on the ___ of the small intestine with ___ & ___

• inside

• villi

• microvilli

Intestinal Crypts

very similar to the gastric pit but have secretion (weak acids and mucus) AND absorption (nutrients) ability

Sections of the Small Intestine

1. duodenum

2. jejunum

3. ilium

Duodenum

receives chyme from the pylorus, bile from gallbladder/liver, and digestive enzymes from liver/pancreas

Jejunum

last region of chemical digestion; lots of segmentation of chyme

Ilium

continued surface area of absorption of nutrients, has “Peyer’s Patches” (clusters of immune cells - last line of defense for GI tract against pathogens)

Large intestine pulls ___ out of feces, but the feces still need to be adequate ___ to exit out the ___ (goblet cells release mucus)

• water

• lubricated

• alimentary canal

Movement of the large intestine are much ___ on average than the small intestine

slower

What makes the large intestine slower

• muscles contract in response to digestion

• muscles contract for ~1 Minute about every ½ hour

• About 3-4 times per day, mass movements occur

  • very large peristaltic contraction that moves feces towards the rectum + anus

  • only occurs if food had been ingested

The Liver

hepato

The liver is one of the ___ organs in the body

largest (w/o it = death within 24 hours)

Liver tissue can

regenerate

Where is the liver located

left side of the body below the diaphragm

Liver cells are called

hepatocytes

Bile Production

chemical digestion of fat

Detoxification

medicine, food, alcohol, etc

Hepatocytes degrade

hormones

Hepatocytes synthesize

certain proteins/ digestive enzymes and blood clotting proteins “TF”

Liver is located under diaphragm and is divided into 4 lobes

1. right

2. left

3. quadrate

4. caudate

Hepatic Portal System

circulatory pattern from the small intestine to the liver

⭐ after nutrients are absorbed into the blood, it must pass through the liver before going anywhere else → know why for test (MC)

O2 Rich Blood

from the heart arrives in capillaries that surround the small intestine

→ small intestine receives O2

→ blood takes in nutrients absorbed by small intestine

O2 Poor Blood

(with lots of nutrients) is sent directly to the liver via the hepatic portal vein

→ liver pulls out pathogens

O2 poor blood leaves the ___ to return to the ___ via the ___

• liver

• heart

• common hepatic vein

2 Primary Functions of the Kidney

1. filter nitrogenous wastes from the blood to be excreted

2. osmoregulation (internal waste balance)